Hygroscopic cooling tower for waste water disposal

ABSTRACT

In various embodiments, the present invention relates to heat dissipation systems including a hygroscopic working fluid integrating waste water as makeup water. The present invention also relates to methods of using the same. The present invention also relates to hygroscopic cooling systems adapted to dispose of waste water by combining the waste water with a hygroscopic working fluid, precipitating impurities and evaporating the remaining water.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. Utility application Ser. No.15/918,916, filed May 12, 2018, which is a continuation-in-part of U.S.Utility application Ser. No. 14/884,450, filed Oct. 15, 2015, which is acontinuation-in-part of U.S. Utility application Ser. No. 13/953,332,filed Jul. 29, 2013, which is a continuation-in-part of U.S. Utilityapplication Ser. No. 13/040,379, filed Mar. 4, 2011, which claims thebenefit of priority to U.S. Provisional Application No. 61/345,864,filed May 18, 2010, the disclosures of which are incorporated herein intheir entireties by reference.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

This invention was made with government support under ContractW912HQ17C0050 awarded by the United States Department of DefenseEnvironmental Security Technology Certification Program. The governmenthas certain rights in the invention.

This invention was made with government support under CooperativeAgreement No. DE-FC26-08NT43291 entitled “EERC-DOE Joint Program onResearch and Development for Fossil Energy-Related Resources,” awardedby the United States Department of Energy (DOE). The government hascertain rights in the invention.

BACKGROUND OF THE INVENTION

Thermal energy dissipation is a universal task in industry that haslargely relied on great quantities of cooling water to satisfy. Commonheat rejection processes include steam condensation in thermoelectricpower plants, refrigerant condensation in air-conditioning andrefrigeration equipment, and process cooling during chemicalmanufacturing. In the case of power plants and refrigeration systems, itis desired to dissipate thermal energy at the lowest possibletemperature with a minimal loss of water to the operating environmentfor optimum resource utilization.

Where the local environment has a suitable, readily available,low-temperature source of water, e.g., a river, sea, or lake, coolingwater can be extracted directly. However, few of these opportunities forcooling are expected to be available in the future because competitionfor water sources and recognition of the impact of various uses of watersources on the environment are increasing. In the absence of a suitable,readily available coolant source, the only other common thermal sinkavailable at all locations is ambient air. Both sensible heat transferand latent heat transfer are currently used to reject heat to the air.In sensible cooling, air is used directly as the coolant for cooling oneside of a process heat exchanger. For latent cooling, liquid water isused as an intermediate heat-transfer fluid. Thermal energy istransferred to the ambient air primarily in the form of evaporated watervapor, with minimal temperature rise of the air.

These technologies are used routinely in industry, but each one hasdistinct drawbacks. In the sensible cooling case, air is an inferiorcoolant compared to liquids, and the resulting efficiency of air-cooledprocesses can be poor. The air-side heat-transfer coefficient inair-cooled heat exchangers is invariably much lower than liquid-cooledheat exchangers or in condensation processes and, therefore, requires alarge heat exchange surface area for good performance. In addition tolarger surface area requirements, air-cooled heat exchangers approachthe cooling limitation of the ambient dry-bulb temperature of the airused for cooling, which can vary 30° to 40° F. over the course of a dayand can hinder cooling capacity during the hottest hours of the day.Air-cooled system design is typically a compromise between processefficiency and heat exchanger cost. Choosing the lowest initial costoption can have negative energy consumption implications for the life ofthe system.

In latent heat dissipation, the cooling efficiency is much higher, andthe heat rejection temperature is more consistent throughout the courseof a day since a wet cooling tower will approach the ambient dew pointtemperature of the air used for cooling instead of the oscillatorydry-bulb temperature of the air used for cooling. The key drawback orproblem associated with this cooling approach is the associated waterconsumption used in cooling, which in many areas is a limiting resource.Water-based cooling requires consumption of water of sufficiently highquality, substantially free of impurities that foul equipment or degradethe process system. This requirement stresses water resources. Obtainingsufficient water rights for wet cooling system operation delays plantpermitting, limits site selection, and creates a highly visiblevulnerability for opponents of new development.

Prior art U.S. Pat. No. 3,666,246 discloses a heat dissipation systemusing an aqueous desiccant solution circulated between the steamcondenser (thermal load) and a direct-contact heat and mass exchanger incontact with an ambient air flow. In this system, the liquid solution isforced to approach the prevailing ambient dry-bulb temperature andmoisture vapor pressure. To prevent excessive drying and precipitationof the hygroscopic desiccant from solution, a portion of the circulatinghygroscopic desiccant flow is recycled back to an air contactor withoutabsorbing heat from the thermal load. This results in a lower averagetemperature in the air contactor and helps to extend the operating rangeof the system.

The recirculation of unheated hygroscopic desiccant solution iseffective for the ambient conditions of approximately 20° C. andapproximately 50% relative humidity as illustrated by the exampledescribed in U.S. Pat. No. 3,666,246, but in drier, less humidenvironments, the amount of unheated recirculation hygroscopic desiccantflow must be increased to prevent crystallization of the hygroscopicdesiccant solution. As the ambient air's moisture content decreases, therequired recirculation flow grows to become a larger and largerproportion of the total flow such that no significant cooling of thecondenser is taking place, thereby reducing the ability of the heatdissipation system to cool, in the extreme, to near zero or nosignificant cooling. Ultimately, once the hygroscopic desiccant is nolonger a stable liquid under the prevalent environmental conditions, noamount of recirculation flow can prevent crystallization of the unheatedhygroscopic desiccant solution.

Using the instantaneous ambient conditions as the approach condition forthe hygroscopic desiccant solution limits operation of the heatdissipation system in U.S. Pat. No. 3,666,246 to a relative humidity ofapproximately 30% or greater with the preferred MgCl₂ hygroscopicdesiccant solution. Otherwise, the hygroscopic desiccant may completelydry out and precipitate from solution. This limitation would excludeoperation and use of the heat dissipation system described in U.S. Pat.No. 3,666,246 in regions of the world that experience significantlydrier weather patterns, less humid air, and are arguably in need ofimprovements to dry cooling technology.

Additionally, while the heat dissipation system described in U.S. Pat.No. 3,666,246 discloses that the system may alternatively be operated toabsorb atmospheric moisture and subsequently evaporate it, the disclosedheat dissipation system design circumvents most of this mode ofoperation of the heat dissipation system. Assuming that atmosphericmoisture has been absorbed into hygroscopic desiccant solution duringthe cooler, overnight hours, evaporation of water from the hygroscopicdesiccant will begin as soon as the ambient temperature begins to warmin the early morning, using the heat dissipation system described inU.S. Pat. No. 3,666,246, since it has no mechanism to curtail excessivemoisture evaporation during the early morning transition period and noway to retain excess moisture for more beneficial use later in the dailycycle, such as afternoon, when ambient temperatures and cooling demandare typically higher. Instead, absorbed water in the hygroscopicdesiccant in the heat dissipation system will begin evaporating as soonas the hygroscopic desiccant solution's vapor pressure of the heatdissipation system exceeds that of the ambient air, regardless ofwhether it is productively dissipating thermal energy from the heat loador wastefully absorbing the energy from the ambient air stream.

Improvements have been proposed to these basic cooling systems.Significant effort has gone into hybrid cooling concepts that augmentair-cooled condensers with evaporative cooling during the hottest partsof the day. These systems can use less water compared to complete latentcooling, but any increased system performance is directly related to theamount of water-based augmentation, so these systems do not solve theunderlying issue of water consumption. Despite the fact that meeting thecooling needs of industrial processes is a fundamental engineering task,significant improvements are still desired, primarily the elimination ofwater consumption while simultaneously maintaining high-efficiencycooling at reasonable cost.

There is a need for improved heat dissipation technology relative tocurrent methods. Sensible cooling with air is costly because of the vastheat exchange surface area required and because its heat-transferperformance is handicapped during the hottest ambient temperatures.Latent or evaporative cooling has preferred cooling performance, but itconsumes large quantities of water which is a limited resource in somelocations.

Turbine inlet chilling (TIC) systems for combustion turbines are used tomaintain the turbine's operating efficiency during extremes of hotweather and even to boost its performance above baseline under lesssevere ambient conditions. To do this, TIC systems employvapor-compression chillers to cool the turbine's incoming ambient air inorder to approach conditions where the turbine is designed to produceits full-load rating. These chillers have a significant heat rejectionload to the environment that is typically dissipated by wet evaporativecooling. While condensed water collection can be 40% of the evaporativemakeup water requirement for a conventional wet cooling tower, this isinsufficient to make the system water-neutral.

Desalination plants are increasingly being installed to diversify watersupply portfolios, improve water supply reliability, and meet watersupply shortages due to drought, climate change and population growth.Typical membrane or thermal desalination processes generate aconcentrated salt stream that contains the majority of the salts andsome of the feed water. Such concentrated salt stream is often referredto as simply concentrate. A major drawback to wide spread adoption ofdesalination for inland areas is the lack of options in handlingconcentrate streams generated from desalination processes. Conventionaldesalination technologies include reverse osmosis (RO), which is themost commonly used desalination technology to treat saline water sourcesin the United States. Other desalination processes, such aselectrodialysis and thermal desalination processes, also produce aconcentrate stream and are more widely used in other parts of the world.Concentrated salt streams produced from desalination plants are aproblematic source of waste which must be managed or disposed. The costto manage or dispose of concentrate streams is often prohibitive and iscurrently a limiting factor to more widespread utilization ofdesalination in inland applications. The following are currentapproaches to concentrate discharge management: direct disposal (surfacedischarge, sewer discharge); evaporation ponds; deep well injection; andtreatment trains comprised of a series of numerous water treatmenttechnologies (crystallizers, evaporators, etc.). Approaches to achievezero liquid concentrate discharge rely on the use of evaporation pondsor thermal treatment processes such as a brine crystallizer. Inevaporation ponds, waste water evaporation is limited by ambientconditions and the process is not suitable for all climates. Althoughcrystallizers have fewer restrictions than evaporation ponds, theyrequire high-grade energy input to boil away or flash the excess waterin order to precipitate the dissolved solids.

SUMMARY OF THE INVENTION

A heat dissipation system apparatus and method of operation usinghygroscopic working fluid for use in a wide variety of environments forabsorbed water in the hygroscopic working fluid to be released tominimize water consumption in the heat dissipation system apparatus foreffective cooling in environments having little available water for usein cooling systems.

In various embodiments, the present invention provides a method for heatdissipation using a hygroscopic working fluid. The method includestransferring thermal energy from a heated process fluid to thehygroscopic working fluid in a process heat exchanger, to form a cooledprocess fluid. The method includes condensing liquid from a feed gas ona heat transfer surface of a feed gas heat exchanger in contact with thecooled process fluid, to form a cooled feed gas, the heated processfluid, and a condensate. The method includes dissipating thermal energyfrom the hygroscopic working fluid to a cooling gas composition with afluid-air contactor. The method includes transferring moisture betweenthe hygroscopic working fluid and the cooling gas composition with thefluid-air contactor. The method includes adding at least part of thecondensate to the hygroscopic working fluid.

In various embodiments, the present invention provides a method for heatdissipation using a hygroscopic working fluid. The method includestransferring thermal energy from a heated process fluid to thehygroscopic working fluid in a process heat exchanger, to form a cooledprocess fluid. The method includes transferring thermal energy from thefeed gas to the cooled process fluid in a feed gas heat exchanger, toform a cooled feed gas and the heated process fluid. The method includesfeeding the cooled feed gas to a combustion turbine. The method includestransferring thermal energy from the hygroscopic working fluid to acooling gas composition with a fluid-air contactor. The method includestransferring moisture between the hygroscopic working fluid and thecooling gas composition with the fluid-air contactor.

In various embodiments, the present invention provides a method for heatdissipation using a hygroscopic working fluid. The method includestransferring thermal energy from a heated process fluid to thehygroscopic working fluid in a chiller, to form a cooled process fluid.The method includes condensing liquid from a feed gas on a heat transfersurface of a feed gas heat exchanger in contact with the cooled processfluid, to form a cooled feed gas, the heated process fluid, and acondensate. The chiller includes a compressor that compresses a chillerworking fluid prior to transferring thermal energy from the compressedchiller working fluid to the hygroscopic working fluid. The chillerincludes a valve that allows the chiller working fluid to expand priorto transferring thermal energy from the heated process fluid to theexpanded chiller working fluid. The method includes feeding the cooledfeed gas to a combustion turbine. The method includes dissipatingthermal energy from the hygroscopic working fluid to a cooling gascomposition with a fluid-air contactor, the cooling gas compositionincluding the ambient atmosphere. The method includes transferringmoisture between the hygroscopic working fluid and the cooling gascomposition with the fluid-air contactor. The method includes adding atleast part of the condensate to the hygroscopic working fluid. Thecondensing of the liquid from the feed gas provides sufficientcondensate to make up for water lost from the hygroscopic working fluidto the cooling gas composition in the fluid-air contactor, providing atleast water-neutral operation.

In various embodiments, the present invention provides a system for heatdissipation using a hygroscopic working fluid. The system includes aprocess heat exchanger configured to transfer thermal energy from aheated process fluid to a hygroscopic working fluid to form a cooledprocess fluid. The system includes a feed gas heat exchanger configuredto condense liquid from a feed gas on a heat transfer surface of thefeed gas heat exchanger in contact with the cooled process fluid, toform a cooled feed gas, the heated process fluid, and a condensate. Thesystem includes a fluid-air contactor configured to dissipate heat fromthe hygroscopic working fluid to a cooling gas composition, andconfigured to transfer moisture between the hygroscopic working fluidand the cooling gas composition. The system is configured to add atleast part of the condensate to the hygroscopic working fluid.

The condenser cooling load of a TIC chiller is on the order of 20% ofthe heat rejection load for an entire natural gas combined cycle powerplant, and since TIC systems are frequently added after initialconstruction, the plant's existing cooling system typically does nothave the extra capacity to accommodate the TIC system. Dry cooling ofTIC systems is desirable because it would eliminate the need to sourceadditional cooling water for the plant. However, the large chillersemployed for TIC are predominantly designed for liquid cooling insteadof using an air-cooled condenser, which results in an inefficient drycooling configuration including a sensible, air-cooled water loop withtwo heat transfer interfaces.

In various embodiments, the present invention provides certainadvantages over other methods of cooling a feed gas, at least some ofwhich are unexpected. For example, performing cooling via use ofdesiccant-based hygroscopic fluid to meet the heat rejection needs of aTIC system can enable efficient and water-neutral TIC operation.

In various embodiments, the preferred climates and/or times day that aremost competitive for TIC enable the use of a less corrosive desiccant,e.g., CaCl₂), that can be used to directly cool the chiller'srefrigerant condenser without the need for an intermediate heatexchanger. Many of the large chillers offer titanium metallurgy which isrecommended for CaCl₂) solutions and eliminating the intermediate heattransfer step can improve the efficiency of condenser cooling. Preferredclimates for TIC include high humidity areas where it is has acompetitive advantage over evaporative turbine inlet cooling. Withthermal storage, TIC condenser cooling demand is transferred to off-peakhours which are inherently cooler. Both of these conditions favor theuse of desiccants like CaCl₂) which are less corrosive, but also lessable to withstand extremely hot and dry conditions.

In various embodiments, condensate from cooling the feed gas (e.g.,turbine inlet air) can be consumed and used to augment the performanceof the desiccant cooling system. This condensate is generally free ofscaling components that could precipitate and foul the desiccant coolingsystem and is an excellent source of water to mix with the desiccant toaugment cooling performance without concerns of introducing a mineralimbalance. Excess water added to the desiccant increases the amount oflatent heat transfer that can take place in the air-desiccant contactor,thereby enabling either lower cold desiccant temperatures or a highercooling capacity. The amount of water recovered as condensate couldexceed 40% of the evaporative makeup water needed by a conventional wetcooling system to cool the TIC system, which would make a sizeablecontribution to the performance of a desiccant-based hygroscopic fluidcooling system, but is far short of the water needed to reachwater-neutral operation with conventional wet cooling. In contrast, invarious embodiments of the method and system for cooling a feed gasusing a hygroscopic working fluid, the condensate collected can be equalto or greater than the amount of water lost from the hygroscopic workingfluid, providing water-neutral operation.

Operating characteristics of the TIC system generally negate thecriticality of using wet cooling. As previously mentioned the preferredclimates and times of operation for TIC coincide with more humid andcooler conditions. These conditions reduce the differential in coolingperformance that can be achieved with conventional wet cooling versus adry system. These characteristics combined with the augmentationpossible by using condensed water from inlet air chilling suggest thatin various embodiments desiccant-based hygroscopic fluid cooling can beapplied to a TIC system, making the process water neutral, with minimalimpact to performance or with better performance compared toconventional wet or dry cooling arrangements.

In various embodiments, the present invention provides a method of wastewater disposal, the method comprising: contacting a hygroscopic workingfluid with a heat exchanger having a heated process fluid; transferringthermal energy from the heated process fluid to the hygroscopic workingfluid and flowing the resulting hygroscopic working fluid from the heatexchanger to a fluid-air contactor having an air stream; contacting thehygroscopic working fluid with the air stream of the fluid-aircontactor; transferring water from the hygroscopic working fluid to theair stream, collecting the resulting hygroscopic working fluid andcirculating it to the process heat exchanger; directing at least aportion of the hygroscopic working fluid to form a mixture with wastewater in a makeup mix tank at conditions to precipitate dissolvedimpurities from the mixture; and filtering the precipitate from themixture to form a filtrate and then directing the filtrate to combinewith the circulating hygroscopic working fluid; wherein the hygroscopicworking fluid comprises a desiccant and water.

In various embodiments, the present invention provides a hygroscopiccooling system, the system comprising: a hygroscopic working fluidcomprising a desiccant and water; a heat exchanger configured totransfer thermal energy from a heated process fluid to the hygroscopicworking fluid; a fluid-air contactor having an air stream, wherein thefluid-air contactor and air-stream are configured to transfer water fromthe hygroscopic working fluid to the air stream; wherein the heatexchanger and the fluid-air contactor are configured so the hygroscopicworking fluid is circulated through the heat exchanger and the fluid-aircontactor; a makeup mix tank configured to receive waste water and atleast some of the circulated hygroscopic working fluid, wherein themakeup mix tank is at conditions which permit the waste water and thehygroscopic working fluid to mix and to precipitate dissolved impuritiesfrom the resulting mixture; and a filter unit configured to removeprecipitated impurities from the mixture of waste water and hygroscopicworking fluid and direct the resulting filtrate to combine with thecirculated hygroscopic working fluid.

There are various advantages to using the methods and systems disclosedherein, at least some of which are unexpected. For example, in variousembodiments, the invention can provide a method and system of disposingof waste water. In various embodiments, the invention can offer anefficient solution for achieving zero liquid discharge requirements byintegrating a hygroscopic cooling process with a process that generateswaste water. For example, the hygroscopic cooling process can beconfigured to accept waste water and the waste water can be permitted tolargely or fully evaporate in the hygroscopic cooling process. As such,the hygroscopic cooling system can be used to dispose of waste water. Asanother advantage, using waste water to support evaporative cooling alsodisplaces higher-quality water that would otherwise be consumed in aconventional cooling tower thus reducing consumption of higher-qualitywater and reducing costs. Thus, the present invention can offer two-foldenvironmental advantages: zero liquid discharge, and reduced need forhigher-quality makeup water. Displacing higher-quality water withlower-quality concentrate frees up higher-quality water resources forproductive uses in other aspects of the overall system. For example, ifreclaimed, non-brackish, non-potable water were used as cooling towermakeup water, displacing it with lower-quality waste water, e.g., saltwater concentrate, would allow the non-brackish, non-potable water to beused for purposes that lower-quality waste water cannot be used, e.g.,irrigation.

In various embodiments, low temperature waste heat resources may be usedto drive evaporation which results in improved efficiency.

In various embodiments, using waste water in a hygroscopic coolingsystem can have improved cost effectiveness compared to hygroscopiccooling systems using higher-quality makeup water, because waste watermay be available at minimal or no cost.

In various embodiments, integrating waste water into a hygroscopiccooling system may induce controlled precipitation of most or all of thedissolved impurities in the waste water. The hygroscopic cooling systemcan be configured to control the location and amount of impurityprecipitation. Such precipitation can advantageously be separated anddisposed. Thus, the hygroscopic cooling system represents a solution tomanaging, processing or disposing of waste water and its constituents.

In various embodiments, integrating waste water into a hygroscopiccooling system has environmental advantages, because use of waste waterreduces the amount of such waste being passed to the environment. Thisadvantage can be achieved without use of any toxic or hazardousmaterials. In various embodiments where dissolved solids areprecipitated and removed, such resulting solid waste represents aminimal volume of waste which greatly simplifies disposal.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic of the heat dissipation system, according tovarious embodiments.

FIG. 2A is a chart depicting the input temperature conditions used tocalculate the dynamic response, according to various embodiments.

FIG. 2B is a chart depicting the calculated components of heat transferof the present invention in response to the cyclical input temperatureprofile of FIG. 2A, according to various embodiments.

FIG. 3 is a schematic of a cross-flow air contactor, according tovarious embodiments.

FIG. 4 is a cross-sectional detail of one of the tube headers shown inthe air contactor of FIG. 3 , according to various embodiments.

FIG. 5A is a schematic of a falling-film process heat exchanger,according to various embodiments.

FIG. 5B is a section view of the process heat exchanger in FIG. 5A asviewed from the indicated section line, according to variousembodiments.

FIG. 6 is a schematic of an embodiment incorporating a falling-filmprocess heat exchanger to precondition the air contactor inlet air,according to various embodiments.

FIG. 7 is a schematic of an embodiment incorporating the air contactorto precondition a falling-film process heat exchanger, according tovarious embodiments.

FIG. 8 is a schematic of an embodiment of the present inventionincorporating alternate means to increase the moisture content of theworking fluid, according to various embodiments.

FIG. 9 is a schematic of an embodiment of the present inventionincorporating staged multiple cross-flow air contactors, according tovarious embodiments.

FIG. 10 illustrates the operation of the embodiment of the presentinvention illustrated in FIG. 9 , according to various embodiments.

FIG. 11 is a schematic of an embodiment of the present inventionincluding an osmosis membrane moisture extraction cell, according tovarious embodiments.

FIG. 12 is a schematic of an embodiment of the present inventionincluding a vacuum evaporator, according to various embodiments.

FIG. 13 illustrates an embodiment of a system that can be used to cool afeed gas using a hygroscopic working fluid, according to variousembodiments.

FIG. 14 is a schematic of an embodiment of the present invention of ahygroscopic cooling system incorporated for use disposing of a blowdownstream from a plant's primary cooling tower, according to variousembodiments.

FIG. 15 is a schematic of an embodiment of the present invention of ahygroscopic cooling system incorporated for use disposing of aconcentrated salt stream from a desalination system, according tovarious embodiments.

FIG. 16 is a schematic of an embodiment of the present invention of ahygroscopic cooling system incorporated for use disposing of a reverseosmosis concentrate from a reverse osmosis system, according to variousembodiments.

FIG. 17 shows the positive saturation index values calculated forspecies of three reverse osmosis concentrate samples, according tovarious embodiments.

FIG. 18A shows calculated maximum solubility values for a dissolvedsolid species, calcium carbonate, in response to increasing desiccantconcentration, according to various embodiments.

FIG. 18B shows calculated maximum solubility values for a dissolvedsolid species, calcium sulfate, in response to increasing desiccantconcentration, according to various embodiments.

FIG. 18C shows calculated maximum solubility values for a dissolvedsolid species, silicon dioxide, in response to increasing desiccantconcentration, according to various embodiments.

FIG. 18D shows calculated maximum solubility values for a highly solubledissolved solid species, sodium chloride, in response to increasingdesiccant concentration, according to various embodiments.

DETAILED DESCRIPTION OF THE INVENTION

Reference will now be made in detail to certain embodiments of thedisclosed subject matter, examples of which are illustrated in part inthe accompanying drawings. While the disclosed subject matter will bedescribed in conjunction with the enumerated claims, it will beunderstood that the exemplified subject matter is not intended to limitthe claims to the disclosed subject matter.

Throughout this document, values expressed in a range format should beinterpreted in a flexible manner to include not only the numericalvalues explicitly recited as the limits of the range, but also toinclude all the individual numerical values or sub-ranges encompassedwithin that range as if each numerical value and sub-range is explicitlyrecited. For example, a range of “about 0.1% to about 5%” or “about 0.1%to 5%” should be interpreted to include not just about 0.1% to about 5%,but also the individual values (e.g., 1%, 2%, 3%, and 4%) and thesub-ranges (e.g., 0.1% to 0.5%, 1.1% to 2.2%, 3.3% to 4.4%) within theindicated range. The statement “about X to Y” has the same meaning as“about X to about Y,” unless indicated otherwise. Likewise, thestatement “about X, Y, or about Z” has the same meaning as “about X,about Y, or about Z,” unless indicated otherwise.

In this document, the terms “a,” “an,” or “the” are used to include oneor more than one unless the context clearly dictates otherwise. The term“or” is used to refer to a nonexclusive “or” unless otherwise indicated.The statement “at least one of A and B” has the same meaning as “A, B,or A and B.” In addition, it is to be understood that the phraseology orterminology employed herein, and not otherwise defined, is for thepurpose of description only and not of limitation. Any use of sectionheadings is intended to aid reading of the document and is not to beinterpreted as limiting; information that is relevant to a sectionheading may occur within or outside of that particular section. A commacan be used as a delimiter or digit group separator to the left or rightof a decimal mark; for example, “0.000.1” is equivalent to “0.0001.” Allpublications, patents, and patent documents referred to in this documentare incorporated by reference herein in their entirety, as thoughindividually incorporated by reference. In the event of inconsistentusages between this document and those documents so incorporated byreference, the usage in the incorporated reference should be consideredsupplementary to that of this document; for irreconcilableinconsistencies, the usage in this document controls.

In the methods described herein, the acts can be carried out in anyorder without departing from the principles of the invention, exceptwhen a temporal or operational sequence is explicitly recited.Furthermore, specified acts can be carried out concurrently unlessexplicit claim language recites that they be carried out separately. Forexample, a claimed act of doing X and a claimed act of doing Y can beconducted simultaneously within a single operation, and the resultingprocess will fall within the literal scope of the claimed process.

The term “about” as used herein can allow for a degree of variability ina value or range, for example, within 10%, within 5%, or within 1% of astated value or of a stated limit of a range, and includes the exactstated value or range.

The term “substantially” as used herein refers to a majority of, ormostly, as in at least about 50%, 60%, 70%, 80%, 90%, 95%, 96%, 97%,98%, 99%, 99.5%, 99.9%, 99.99%, or at least about 99.999% or more, or100%.

The heat dissipation systems described herein are an improvement to thestate of the art in desiccant-based (hygroscopic) fluid cooling systemsby incorporating means to regulate the amount of sensible heat transfer,e.g., heat exchanged having as its sole effect a change of temperatureversus latent heat transfer, e.g., heat exchanged without change oftemperature, taking place in heat dissipation system so that thedesiccant-based hygroscopic fluid remains stable (hygroscopic desiccantin solution) to prevent crystallization of the desiccant from thedesiccant-based hygroscopic fluid. In simple form, the heat dissipationsystem includes at least one hygroscopic desiccant-to-air direct-contactheat exchanger for heat exchange having combined sensible and latentheat transfer, at least one sensible heat exchanger for heat exchangewith a change of temperature of the heat exchange fluid used, and atleast one desiccant (hygroscopic) fluid for use as the heat exchangefluid in the heat dissipation system to exchange water with theatmosphere to maintain the water content of the desiccant (hygroscopic)fluid. In the heat dissipation systems described herein, thermal energyis dissipated at a higher (but still allowable) temperature duringcooler ambient periods in order to maintain cooling capacity during peakambient temperatures. In some embodiments, preventing crystallization ofthe desiccant includes preventing substantially all crystallization ofthe desiccant. In some embodiments, preventing crystallization of thedesiccant can include substantially preventing crystallization of thedesiccant but allowing less than a particular small amount ofcrystallization to occur, for example, wherein no more than about0.000.000.001 wt % or less of the desiccant present in solutioncrystallizes, or such as no more than about 0.000.000.01, 0.000.000.1,0.000.001, 0.000.01, 0.000.1, 0.001, 0.01, 0.1, 1, 1, 1.5, 2, 3, 4, 5 wt%, or no more than about 10 wt % of the desiccant present in solutioncrystallizes.

In various embodiments, the heat dissipation systems described hereincan include staged sequences of the direct-contact air-fluid latent heatexchangers and sensible heat exchangers that interface with the thermalload, wherein the heat exchangers can have any flow arrangement, such ascounterflowing, cross flowing, or any other suitable arrangement.Feedback from one stage of the direct-contact air-fluid latent heatexchanger is passed to another stage of the direct-contact air-fluidlatent heat exchanger in the form of increased vapor pressure in the airstream and reduced temperature of the hygroscopic desiccant workingfluid servicing the thermal load. Combined, such staged sequences of thedirect-contact air-fluid latent exchangers and the sensible heatexchangers that interface with the thermal load reduce the proportion ofthe thermal load passed to the initial, cooler stages of thedirect-contact air-fluid latent heat exchangers (which contain much ofthe moisture absorbed during cooler periods) and prevent excessiveevaporation from the final, hotter stages of the direct-contactair-fluid latent heat exchangers.

The heat dissipation systems described herein each circulate at leastone (or multiple differing types of) hygroscopic working fluid totransfer heat from a process requiring cooling directly to the ambientair. The hygroscopic fluid is in liquid phase at conditions in which itis at thermal and vapor pressure equilibrium with the expected localambient conditions so that the desiccant-based hygroscopic fluid remainsstable to prevent crystallization of the desiccant from thedesiccant-based hygroscopic fluid. The hygroscopic fluid includes asolution of a hygroscopic substance and water. In one embodiment, thehygroscopic substance itself should have a very low vapor pressurecompared to water in order to prevent significant loss of thehygroscopic component of the fluid during cycle operation. Thehygroscopic component can be a pure substance or a mixture of substancesselected from compounds known to attract moisture vapor and form liquidsolutions with water that have reduced water vapor pressures. Thehygroscopic component includes all materials currently employed fordesiccation operations or dehumidifying operations, includinghygroscopic inorganic salts, such as LiCl, LiBr, CaCl₂), ZnCl₂;hygroscopic organic compounds, such as ethylene glycol, propyleneglycol, triethylene glycol; or inorganic acids, such as H₂SO₄ and thelike.

Thermal energy is removed from the process in a suitable sensible heatexchanger having on one side thereof, the flow of process fluid, and onthe other side thereof, the flow of hygroscopic working fluid coolant.This sensible heat exchanger can take the form of any well-known heatexchange device, including shell-and-tube heat exchangers,plate-and-frame heat exchangers, or falling-film heat exchangers. Theprocess fluid being cooled includes a single-phase fluid, liquid, or gasor can be a fluid undergoing phase change, e.g., condensation of a vaporinto a liquid. Consequently, the thermal load presented by thehygroscopic process fluid can be sensible, e.g., with a temperaturechange, or latent which is isothermal. Flowing through the other side ofthe sensible heat exchange device, the hygroscopic working fluid coolantcan remove heat sensibly, such as in a sealed device with no vaporspace, or it can provide a combination of sensible and latent heatremoval if partial evaporation of the moisture in solution is allowed,such as in the film side of a falling-film type heat exchanger.

After thermal energy has been transferred from the process fluid to thehygroscopic working fluid using the sensible heat exchanger, thehygroscopic fluid is circulated to an air-contacting latent heatexchanger where it is exposed directly to ambient air for heatdissipation. The latent heat exchanger is constructed in such a way asto generate a large amount of interfacial surface area between thedesiccant solution and air. Any well-known method may be used togenerate the interfacial area, such as by including a direct spray ofthe liquid into the air, a flow of hygroscopic solution distributed overrandom packings, or a falling film of hygroscopic liquid solution down astructured surface. Flow of the air and hygroscopic desiccant solutionstreams can be conducted in the most advantageous way for a particularsituation, such as countercurrent where the hygroscopic desiccantsolution may be flowing down by gravity and the air is flowing up,crossflow where the flow of hygroscopic desiccant solution is in anorthogonal direction to airflow, cocurrent where the hygroscopicdesiccant solution and air travel in the same direction, or anyintermediary flow type.

Heat- and mass-transfer processes inside the latent heat exchanger areenhanced by convective movement of air through the latent heatexchanger. Convective flow may be achieved by several different means ora combination of such different means. The first means for convectiveairflow is through natural convection mechanisms such as by the buoyancydifference between warmed air inside the latent heat exchanger and thecooler and the surrounding ambient air. This effect would naturallycirculate convective airflow through a suitably designed chamber inwhich the air is being heated by the warmed solution in the latent heatexchanger. Another means for convective airflow includes the forced flowof air generated by a fan or blower for flowing air through the latentheat exchanger. A further convective airflow means includes inducingairflow using momentum transfer from a jet of solution pumped out atsufficient mass flow rate and velocity into the latent heat exchanger.

Inside the latent heat exchanger, an interrelated process of heat andmass transfer occurs between the hygroscopic solution used as theworking fluid and the airflow that ultimately results in the transfer ofthermal energy from the solution to the air. When the air andhygroscopic solution are in contact, they will exchange moisture massand thermal energy in order to approach equilibrium, which for ahygroscopic liquid and its surrounding atmosphere requires a match oftemperature and water vapor pressure. Since the hygroscopic solution'svapor pressure is partially dependent on temperature, the condition isoften reached where the hygroscopic solution has rapidly reached itsequivalent dew point temperature by primarily latent heat transfer (tomatch the ambient vapor pressure), and then further evaporation orcondensation is limited by the slower process of heat transfer betweenthe air and the hygroscopic solution (to match the ambient temperature).

The net amount of heat and mass transfer within the latent heatexchanger is dependent on the specific design of the latent heatexchanger and the inlet conditions of the hygroscopic solution and theambient air. However, the possible outcomes as hygroscopic solutionpasses through the latent heat exchanger include situations where thehygroscopic solution can experience a net loss of moisture (a portion ofthe thermal energy contained in the solution is released as latent heatduring moisture evaporation; this increases the humidity content of theairflow), the hygroscopic solution can experience a net gain in moisturecontent (such occurs when the vapor pressure in the air is higher thanin the solution, and moisture is absorbed by the hygroscopic solutionhaving the latent heat of absorption released into the hygroscopicsolution and being transferred sensibly to the air), and the hygroscopicsolution is in a steady state where no net moisture change occurs (anyevaporation being counterbalanced by an equivalent amount ofreabsorption, or vice versa).

After passing through the latent heat exchanger, the hygroscopicsolution has released thermal energy to the ambient air either throughsensible heat transfer alone or by a combination of sensible heattransfer and latent heat transfer (along with any concomitant moisturecontent change). The hygroscopic solution is collected in a reservoir,the size of which will be selected to offer the best dynamic performanceof the overall cooling system for a given environmental location andthermal load profile. It can be appreciated that the reservoir can alterthe time constant of the cooling system in response to dynamic changesin environmental conditions. For example, moisture absorption in theambient atmosphere will be most encouraged during the night and earlymorning hours, typically when diurnal temperatures are at a minimum, andan excess of moisture may be collected. On the other extreme, moistureevaporation in the ambient atmosphere will be most prevalent during theafternoon when diurnal temperatures have peaked, and there could be anet loss of hygroscopic solution moisture content. Therefore, for acontinuously operating system in the ambient atmosphere, the reservoirand its method of operation can be selected so as to optimize thestorage of excess moisture gained during the night so that it can beevaporated during the next afternoon, to maintain cooling capacity andensure that the desiccant-based hygroscopic fluid remains stable toprevent crystallization of the hygroscopic desiccant from thedesiccant-based hygroscopic fluid.

The reservoir itself can be a single mixed tank where the averageproperties of the solution are maintained. The reservoir also includes astratified tank or a series of separate tanks intended to preserve thedistribution of water collection throughout a diurnal cycle so thatcollected water can be metered out to provide maximum benefit.

The present heat dissipation system includes the use of a hygroscopicworking fluid to remove thermal energy from a process stream anddissipate it to the atmosphere by direct contact of the working fluidand ambient air. This enables several features that are highlybeneficial for heat dissipation systems, including 1) using the workingfluid to couple the concentrated heat-transfer flux in the process heatexchanger to the lower-density heat-transfer flux of ambient air heatdissipation, 2) allowing for large interfacial surface areas between theworking fluid and ambient air, 3) enhancing working fluid-airheat-transfer rates with simultaneous mass transfer, and 4) moderatingdaily temperature fluctuations by cyclically absorbing and releasingmoisture vapor from and to the air.

Referring to drawing FIG. 1 , one embodiment of a heat dissipationsystem 10 is illustrated using a hygroscopic working fluid 1 in storagereservoir 2 drawn by pump 3 and circulated through process sensible heatexchanger 4. In the process heat exchanger, the hygroscopic workingfluid removes thermal energy from the process fluid that enters hot-sideinlet 5 and exits through hot-side outlet 6. The process fluid can be asingle phase (gas or liquid) that requires sensible cooling or it couldbe a two-phase fluid that undergoes a phase change in the process heatexchanger, e.g., condensation of a vapor into a liquid.

After absorbing thermal energy in process heat exchanger 4, thehygroscopic working fluid is routed to distribution nozzles 7 where itis exposed in a countercurrent fashion to air flowing through aircontactor latent heat exchanger 8. Ambient airflow through the aircontactor in drawing FIG. 1 is from bottom ambient air inlet 9vertically to top air outlet 11 and is assisted by the buoyancy of theheated air and by powered fan 13. Distributed hygroscopic working fluid12 in the air contactor flows down, countercurrent to the airflow by thepull of gravity. At the bottom of air contactor latent heat exchanger 8,the hygroscopic working fluid is separated from the inlet airflow and isreturned to stored solution 1 in reservoir 2.

In air contactor latent heat exchanger 8, both thermal energy andmoisture are exchanged between the hygroscopic working fluid and theairflow, but because of the moisture retention characteristics of thehygroscopic solution working fluid, complete evaporation of thehygroscopic working fluid is prevented and the desiccant-basedhygroscopic working fluid remains stable (hygroscopic desiccant insolution) to prevent crystallization of the desiccant from thedesiccant-based hygroscopic fluid.

If the heat dissipation system 10 is operated continuously withunchanging ambient air temperature, ambient humidity, and a constantthermal load in process sensible heat exchanger 4, a steady-statetemperature and concentration profile will be achieved in air contactorlatent heat exchanger 8. Under these conditions, the net moisturecontent of stored hygroscopic working fluid 1 will remain unchanged.That is not to say that no moisture is exchanged between distributedhygroscopic working fluid 12 and the airflow in air contactor latentheat exchanger 8, but it is an indication that any moisture evaporatedfrom hygroscopic working fluid 12 is reabsorbed from the ambient airflowbefore the hygroscopic solution is returned to reservoir 2.

However, prior to reaching the aforementioned steady-state condition andduring times of changing ambient conditions, heat dissipation system 10may operate with a net loss or gain of moisture content in hygroscopicworking fluid 1. When operating with a net loss of hygroscopic workingfluid moisture, the equivalent component of latent thermal energycontributes to the overall cooling capacity of the heat dissipationsystem 10. In this case, the additional cooling capacity is embodied bythe increased moisture vapor content of airflow 11 exiting air contactorlatent heat exchanger 8.

Conversely, when operating with a net gain of hygroscopic working fluidmoisture (water) content, the equivalent component of latent thermalenergy must be absorbed by the hygroscopic working fluid and dissipatedto the airflow by sensible heat transfer. In this case, the overallcooling capacity of the heat dissipation system 10 is diminished by theadditional latent thermal energy released to the hygroscopic workingfluid. Airflow 11 exiting air contactor latent heat exchanger 8 will nowhave a reduced moisture content compared to inlet ambient air 9.

As an alternative embodiment of heat dissipation system 10 illustratedin drawing FIG. 1 , the heat dissipation system 10 uses thesupplementation of the relative humidity of inlet ambient air 9 withsupplemental gas stream 40 entering through supplemental gas streaminlet 41. When used, gas stream 40 can be any gas flow containingsufficient moisture vapor including ambient air into which water hasbeen evaporated either by misting or spraying, an exhaust stream from adrying process, an exhaust stream of high-humidity air displaced duringventilation of conditioned indoor spaces, an exhaust stream from a wetevaporative cooling tower, or a flue gas stream from a combustion sourceand the associated flue gas treatment systems. The benefit of usingsupplemental gas stream 40 is to enhance the humidity level in aircontactor latent heat exchanger 8 and encourage absorption of moistureinto dispersed hygroscopic working fluid 12 in climates having lowambient humidity. It is also understood that supplemental gas stream 40would only be active when moisture absorption is needed to provide a netbenefit to cyclic cooling capacity, e.g., where the absorbed moisturewould be evaporated during a subsequent time of peak cooling demand orwhen supplemental humidity is needed to prevent excessive moisture(water) loss from the hygroscopic working fluid so that thedesiccant-based hygroscopic fluid remains stable (hygroscopic desiccantin solution) to prevent crystallization of the desiccant from thedesiccant-based hygroscopic fluid.

With the operation of the heat dissipation system 10 described hereinand the effects of net moisture change set forth, the performancecharacteristics of cyclic operation can be appreciated. Illustrated indrawing FIG. 2A is a plot of the cyclic input conditions of ambient airdry-bulb temperature and dew point temperature. The cycle has a periodof 24 hours and is intended to be an idealized representation of adiurnal temperature variation. The moisture content of the air isconstant for the input data of drawing FIG. 2A since air moisturecontent does not typically vary dramatically on a diurnal cycle.

Illustrated in drawing FIG. 2B is the calculated heat-transfer responseof the present invention corresponding to the input data of drawing FIG.2A. The two components of heat transfer are sensible heat transfer andlatent heat transfer, and their sum represents the total coolingcapacity of the system. As shown in drawing FIG. 2B, the sensiblecomponent of heat transfer (Q_(sensible)) varies out of phase with theambient temperature since sensible heat transfer is directlyproportional to the hygroscopic working fluid and the airflowtemperature difference (all other conditions remaining equal). Inpractice, a conventional air-cooled heat exchanger is limited by thisfact. In the case of a power plant steam condenser, this is the leastdesirable heat-transfer limitation since cooling capacity is at aminimum during the hottest part of the day, which frequently correspondsto periods of maximum demand for power generation.

The latent component of heat transfer illustrated in drawing FIG. 2B(Q_(latent)) is dependent on the ambient moisture content and themoisture content and temperature of the hygroscopic working fluid.According to the sign convention used in drawing FIG. 2B, when thelatent heat-transfer component is positive, evaporation is occurringwith a net loss of moisture, and the latent thermal energy is dissipatedto the ambient air; when the latent component is negative, thehygroscopic solution is absorbing moisture, and the latent energy isbeing added to the working fluid, thereby diminishing overall coolingcapacity. During the idealized diurnal cycle illustrated in drawing FIG.2A, the latent heat-transfer component illustrated in drawing FIG. 2Bindicates that moisture absorption and desorption occur alternately asthe ambient temperature reaches the cycle minimum and maximum,respectively. However, over one complete cycle, the net water transferwith the ambient air is zero, e.g., the moisture absorbed during thenight equals the moisture evaporated during the next day, so there is nonet water consumption.

The net cooling capacity of the heat dissipation system 10 isillustrated in drawing FIG. 2B as the sum of the sensible and latentcomponents of heat transfer (Q_(sensible)+Q_(latent)). As illustrated,the latent component of heat transfer acts as thermal damping for theentire system by supplementing daytime cooling capacity with evaporativecooling, region E₁ illustrated in drawing FIG. 2B. This evaporative heattransfer enhances overall heat transfer by compensating for decliningsensible heat transfer during the diurnal temperature maximum, regionE₂. This is especially beneficial for cases like a power plant steamcondenser where peak conversion efficiency is needed during the hottestparts of the day.

The cost of this boost to daytime heat transfer comes at night when theabsorbed latent energy, region E₃, is released into the working fluidand must be dissipated to the airflow. During this time, the totalsystem cooling capacity of heat dissipation system 10 is reduced by anequal amount from its potential value, region E₄. However, this can beaccommodated in practice since the nighttime ambient temperature is lowand overall heat transfer is still acceptable. For a steam power plant,the demand for peak power production is also typically at a minimum atnight.

Regarding air contactor heat exchanger configuration, direct contact ofthe hygroscopic working fluid and surrounding air allows the creation ofsignificant surface area with fewer material and resource inputs thanare typically required for vacuum-sealed air-cooled condensers orradiators. The solution-air interfacial area can be generated by anymeans commonly employed in industry, e.g., spray contactor heatexchanger, wetted packed bed heat exchanger (with regular or randompackings), or a falling-film contactor heat exchanger.

Air contactor heat exchanger 8, illustrated in drawing FIG. 1 , isillustrated as a counterflow spray contactor heat exchanger. While thespray arrangement is an effective way to produce significant interfacialsurface area, in practice such designs can have undesirable entrainedaerosols carried out of the spray contactor heat exchanger by theairflow. An alternate embodiment of the air contactor heat exchanger toprevent entrainment is illustrated in drawing FIG. 3 , which is acrossflow, falling-film contactor heat exchanger designed to minimizedroplet formation and liquid entrainment. Particulate sampling acrosssuch an experimental device has demonstrated that there is greatlyreduced propensity for aerosol formation with this design.

Illustrated in drawing FIG. 3 , inlet hygroscopic working fluid 14 ispumped into distribution headers at the top of falling-film contactorheat exchanger 16. Referring to drawing FIG. 4 , which is a crosssection of an individual distribution header, hygroscopic working fluid17 is pumped through distribution holes 18 located approximatelyperpendicular (at 90°) to the axis of tube header 19 where it wetsfalling-film wick 20 constructed from a suitable material such as wovenfabric, plastic matting, or metal screen. Film wick support 21 is usedto maintain the shape of each wick section. Illustrated in drawing FIG.3 , distributed film 22 of the hygroscopic working fluid solution flowsdown by gravity all of the way to the surface of working fluid 23 inreservoir 24. Inlet airflow 25 flows horizontally through the aircontactor between falling-film sheets 26. In the configurationillustrated in drawing FIG. 3 , heat and mass transfer take placebetween distributed film 22 of hygroscopic working fluid and airflow 25between falling-film sections 26. While drawing FIG. 3 illustrates acrossflow configuration, it is understood that countercurrent,cocurrent, or mixed flow is also possible with this configurationprovided that the desiccant-based hygroscopic fluid remains stable(hygroscopic desiccant in solution) to prevent crystallization of thedesiccant from the desiccant-based hygroscopic fluid.

Illustrated in drawing FIG. 1 , the process heat sensible exchanger 4can assume the form of any indirect sensible heat exchanger known in theart such as a shell-and-tube or plate-type exchanger. One specificembodiment of the sensible heat exchanger that is advantageous for thisservice is the falling-film type heat exchanger. Illustrated in drawingFIG. 5A is a schematic of alternate embodiment process heat exchanger27. Illustrated in drawing FIG. 5B is a cross-sectional view of processheat exchanger 27 viewed along the indicated section line in drawingFIG. 5A. Referring to drawing FIG. 5B, process fluid 28 (which is beingcooled) is flowing within tube 29. Along the top of tube 29, coolhygroscopic working fluid 30 is distributed to form a film surface whichflows down by gravity over the outside of tube 29. Flowing past thefalling-film assembly is airflow 31 which is generated either by naturalconvection or by forced airflow from a fan or blower.

As hygroscopic working fluid 30 flows over the surface of tube 29, heatis transferred from process fluid 28 through the tube wall and into thehygroscopic working fluid film by conduction. As the film is heated, itsmoisture vapor pressure rises and may rise to the point that evaporationtakes place to surrounding airflow 31, thereby dissipating thermalenergy to the airflow. Falling-film heat transfer is well known in theart as an efficient means to achieve high heat-transfer rates with lowdifferential temperatures. One preferred application for thefalling-film heat exchanger is when process fluid 28 is undergoing aphase change from vapor to liquid, as in a steam condenser, wheretemperatures are isothermal and heat flux can be high.

A further embodiment of the heat dissipation system 10 is illustrated indrawing FIG. 6 . The heat dissipation system 10 incorporates thefilm-cooled process sensible heat exchanger to condition a portion ofthe airflow entering air contactor latent heat exchanger 8. Illustratedin drawing FIG. 6 , process sensible heat exchanger 32 is cooled by afalling film of hygroscopic working fluid inside housing 33. Ambient air34 is drawn into process sensible heat exchanger housing 33 and flowspast the film-cooled heat exchanger where it receives some quantity ofevaporated moisture from the hygroscopic fluid film. The higher-humidityairflow at 35 is conducted to inlet 36 of air contactor latent heatexchanger 8 where the airflow 35 is flowing countercurrent to the sprayof hygroscopic working fluid 12. Additional ambient air may also beintroduced to the inlet of air contactor latent heat exchanger 8 throughalternate opening 38.

In the embodiment illustrated in drawing FIG. 6 , moisture vaporreleased from process sensible heat exchanger 32 is added to the aircontactor's inlet airstream and thereby increases the moisture contentby a finite amount above ambient humidity levels. This effect will tendto inhibit moisture evaporation from hygroscopic working fluid 12 andwill result in a finite increase to the steady-state moisture content ofreservoir hygroscopic solution 1 so that the desiccant-based hygroscopicfluid remains stable (hygroscopic desiccant in solution) to preventcrystallization of the desiccant from the desiccant-based hygroscopicfluid. The embodiment illustrated in drawing FIG. 6 may be preferred inarid environments and during dry weather in order to counteractexcessive evaporation of moisture from the hygroscopic working fluid.

A further embodiment of the heat dissipation system 10 is illustrated indrawing FIG. 7 . The heat dissipation system 10 incorporates the aircontactor latent heat exchanger 8 to condition the airflow passing thefilm-cooled process sensible heat exchanger 33. As illustrated indrawing FIG. 7 , a portion of the airflow exiting air contactor latentheat exchanger 8 at outlet 39 is conducted to the inlet of process heatexchanger housing 33. This airflow then flows past film-cooled processsensible heat exchanger 32 where it receives moisture from hygroscopicfilm moisture evaporation.

During high ambient humidity conditions when the net moisture vaporcontent of reservoir hygroscopic solution 1 is increasing, the air atoutlet 39 will have lower moisture vapor content than the moisture vaporcontent of ambient air 9 entering the air contactor latent heatexchanger 8. Therefore, some advantage will be gained by exposingfilm-cooled process sensible heat exchanger 32 to this lower-humidityairstream from outlet 39 rather than the higher-humidity ambient air.The lower-humidity air will encourage evaporation and latent heattransfer in film-cooled sensible process heat exchanger 32. Theembodiment illustrated in drawing FIG. 7 may be preferred forhigh-humidity conditions since it will enhance the latent component ofheat transfer when a film-cooled process heat exchanger, such as 32, isused. However, in any event, during operation of the heat dissipationsystem 10, the desiccant-based hygroscopic fluid remains stable(hygroscopic desiccant in solution) to prevent crystallization of thedesiccant from the desiccant-based hygroscopic fluid.

A further embodiment of the heat dissipation system 10 is illustrated indrawing FIG. 8 . The heat dissipation system 10 uses an alternate meansfor increasing the hygroscopic working fluid moisture content abovethose that could be obtained by achieving equilibrium with the ambientair. The first alternative presented in drawing FIG. 8 is to increasethe moisture content of hygroscopic working fluid 1 directly by additionof liquid water stream 42. In the other alternative presented,hygroscopic working fluid 1 is circulated through absorber latent heatexchanger 43 where it is exposed to gas stream 44. Gas stream 44 hashigher moisture vapor availability compared to ambient air 9. Therefore,the hygroscopic working fluid that passes through absorber latent heatexchanger 43 is returned to reservoir 2 having a higher moisture contentthan that achievable in air contactor latent heat exchanger 8. Thesource of gas stream 44 may include ambient air into which water hasbeen evaporated either by misting or spraying, an exhaust stream from adrying process, an exhaust stream of high-humidity air displaced duringventilation of conditioned indoor spaces, an exhaust stream from a wetevaporative cooling tower, or a flue gas stream from a combustion sourceand the associated flue gas treatment systems. The benefit of suchalternatives illustrated in drawing FIG. 8 is to increase the moisturecontent of hygroscopic working fluid 1 during periods of low heatdissipation demand, such as at night, for the purpose of providingadditional latent cooling capacity during periods when heat dissipationdemand is high so that the desiccant-based hygroscopic fluid remainsstable (hygroscopic desiccant in solution) to prevent crystallization ofthe desiccant from the desiccant-based hygroscopic fluid.

Referring to drawing FIG. 9 , a further embodiment of heat dissipationsystem 100 of the present invention is illustrated using staged multiplecrossflow air contactor, direct-contact latent heat exchangers 102 and103. This embodiment of the present invention includes means to regulatethe amount of sensible heat transfer versus latent heat transfer takingplace in heat dissipation system 100. In this embodiment of theinvention, thermal energy is dissipated at a higher (but stillallowable) temperature during cooler ambient periods in order tomaintain cooling capacity during peak ambient temperatures.

This embodiment of the heat dissipation system 100 of the invention usesstaged sequences of crossflow air contactor heat exchangers 102 and 103used in conjunction with the process sensible heat exchangers 106 and107 that interface with the thermal load. Feedback from one stage ispassed to adjacent stages in the form of increased vapor pressure in airstreams 101 and reduced temperature of the hygroscopic working fluids104, 105 servicing the thermal load. Combined, these mechanisms reducethe proportion of the thermal load passed to the initial, cooler stage102 (which contains much of the moisture absorbed during cooler periods)and prevent excessive evaporation from the final, hotter stage 103.

As illustrated in drawing FIG. 9 , the staged configuration heatdissipation system 100 utilizes a flow of ambient air 101 that entersthe desiccant-to-air crossflow air contactor heat exchanger and passesthrough the first stage of liquid-air contact 102, and subsequentlythrough the second stage of liquid-air contact 103. Contacting sections102 and 103 are depicted as crossflow air contactor latent heatexchangers having liquid film-supporting media that is wetted with fluiddrawn from reservoirs 104 and 105, respectively. The fluid to be cooledenters the system at 108 and first enters sensible heat exchanger 106where it undergoes heat transfer with desiccant solution from thesecond-stage reservoir 105. The partially cooled fluid then enters heatexchanger 107 where it undergoes further heat transfer with desiccantsolution from the first-stage reservoir 104.

Key characteristics of this embodiment of the invention include 1)substantially separate working fluid circuits that allow a desiccantconcentration gradient to become established between the circuits; 2)each circuit has means for direct contact with an ambient airflow streamwhich allows heat and mass transfer to occur, and each circuit has meansfor indirect contact with the fluid to be cooled so that sensible heattransfer can occur; 3) sequential contact of the airflow with eachdesiccant circuit stage; 4) sequential heat exchange contact of eachdesiccant circuit with the fluid to be cooled such that the sequentialdirection of contact between the fluid to be cooled is counter to thedirection of contact for the ambient air flow; and finally, 5) theability to vary the distribution of the heat load among the circuits soas to maximize the amount of reversible moisture cycling by the initialcircuit(s) while preventing crystallization of the desiccant from thedesiccant-based hygroscopic fluid.

The method of direct air-desiccant solution contact can be conductedusing any known-in-the-art heat exchanger, including a spray contactorheat exchanger, falling-film heat exchanger, or wetted structured fillmedia heat exchanger provided that the desiccant-based hygroscopic fluidremains stable (hygroscopic desiccant in solution) to preventcrystallization of the desiccant from the desiccant-based hygroscopicfluid. A preferred embodiment incorporates falling-film media heatexchanger, 102 and 103, operating in a crossflow configuration. Theattached film prevents the formation of fine droplets or aerosols thatcould be carried out with the air stream as drift, while the crossflowconfiguration allows for convenient segregation of the desiccantcircuits.

An illustration of one example of operation of the heat dissipationsystem 100, illustrated in drawing FIG. 9 , is illustrated in drawingFIG. 10 , that is a plot of the heat-transfer components for a two-stageheat dissipation system 100 using desiccant solution in both stages. Inreference to drawing FIG. 9 , contacting section 102 would include Stage1, and contacting section 103 would include stage 2. Each stage of theheat dissipation system 100 has sensible and latent components of heattransfer; the sensible component for Stage 1 is identified as 110, andthe Stage 1 latent component is 111. The sensible heat-transfercomponent and latent heat-transfer component for Stage 2 are identifiedas 112 and 113, respectively. The total sensible heat rejected by thethermal load is constant for this example and is identified as 114;furthermore, it serves as the normalizing factor for all of the otherheat-transfer components and has a value of 1 kW/kW. This is the thermalload transferred to the cooling system in heat exchangers 106 and 107 indrawing FIG. 9 . The final heat-transfer component in drawing FIG. 10 isthe sensible heat transferred to the air stream 115 as would bedetermined from the temperature change of the air across both stages ofdirect-contact media in drawing FIG. 9 .

The phases of operation depicted in drawing FIG. 10 can be distinguishedbased on the distribution of the total thermal load 114, among Stages 1and 2, e.g., 110 and 112, respectively. Around 6:00 as illustrated indrawing FIG. 10 , this ratio is at a minimum; almost the entire thermalload is being sensibly dissipated by Stage 2 and very little in Stage 1.However, during this period, the hygroscopic fluid in Stage 1 is beingrecharged by absorbing moisture from the atmosphere as indicated by thenegative latent heat value at this time (111). The associated heat ofabsorption is rejected to the atmosphere in addition to the constantthermal load (114) as indicated by the air sensible heat transfer (115)being higher than the total thermal load.

Between approximately 8:00 and 16:00 as illustrated in drawing FIG. 10 ,more of the thermal load is transferred from Stage 2 to Stage 1 as theambient dry-bulb temperature begins to rise. The profile of thisprogressive transfer of thermal load is chosen to maintain the desiredcooling capacity and to control the evaporation of the atmosphericmoisture previously absorbed in the Stage 1 hygroscopic fluid. Given therapid nature of evaporative cooling compared to sensible heat transfer,the thermal load is gradually introduced to Stage 1 in order to obtainmaximum benefit of the absorbed moisture, which in drawing FIG. 10occurs at approximately 14:00 or midafternoon, typically when ambientair temperatures peak for the day. Also at this time, the sensible heattransfer to the air is at a minimum because a portion of the thermalload is being dissipated through the latent cooling, primarily in Stage1.

At approximately 18:00, as illustrated in drawing FIG. 10 , the ratio ofStage 1 to Stage 2 sensible heat transfer is at a maximum; beyond thistime, the thermal load is progressively shifted back to Stage 2 as theambient dry-bulb temperature cools. Transferring heat load from theStage 1 hygroscopic fluid also allows it to cool and begin to reabsorbmoisture from the air.

Operation in the manner described cycles the desiccant solution in Stage1 between the extreme conditions of 1) minimal thermal load withsimultaneous exposure to the minimum daily ambient temperatures and 2)maximum thermal load with exposure to peak daily ambient temperatures.This arrangement increases the mass of water that is reversiblyexchanged in the Stage 1 fluid per unit mass of desiccant in the system.Without such “stretching” of the desiccant solution's moisture capacity,an excessively large quantity of solution would be needed to provide thesame level of latent-based thermal energy storage.

Moisture vapor absorption and desorption from Stage 1 consequentlydecreases or increases the vapor pressure experienced at Stage 2, whichdepresses the latent heat transfer of Stage 2 (item 113). Therefore, theimportance of utilizing the Stage 2 hygroscopic fluid as a thermalstorage medium is greatly diminished, and the needed quantity of thishygroscopic fluid is reduced compared to the hygroscopic fluid of Stage1.

The daily pattern of ambient air temperatures is not as regular andpredictable as that used for the simulation results of drawing FIG. 10 .However, the value of this embodiment of the heat dissipation system 10of the invention is that it is a method to alter the time constant forthe cooling system so that cyclic variations having a period on theorder of 24 hours and amplitude on the order of those typicallyencountered in ambient weather can be dampened, and the amount of latentheat transfer is controlled so as to prevent crystallization of thedesiccant from the desiccant-based hygroscopic fluid.

While the diagram of drawing FIG. 9 shows only two distinct stages ofair contacting and thermal load heat transfer, it is understood that theconcept can be extended to include multiple sequences of such stages andthat the general conditions just outlined would apply individually toany two subsequent stages or, more broadly, across an entire systembetween a set of initial contacting stages and a set of followingstages.

In the outlined mode of operation, the maximum water-holding capacity isreached when the initial stage(s) have a relatively lower desiccantconcentration compared to the following stage(s). The series of stagescould contain the same desiccant maintained in a stratified fashion soas to maintain a distinct concentration gradient. Alternatively, theseparate stages could employ different desiccant solutions in order tomeet overall system goals, including moisture retention capacity andmaterial costs. However, in any event, during operation of the entireheat dissipation system 100, the desiccant-based hygroscopic fluid ofeach stage must remain stable (hygroscopic desiccant in solution) toprevent crystallization of the desiccant from the desiccant-basedhygroscopic fluid.

A further embodiment of the heat dissipation system 100 of the presentinvention occurs where the primary stage circuit contains pure water andonly the subsequent following stage(s) contain a hygroscopic desiccantsolution. In this configuration of the heat dissipation system 100 ofthe present invention, the previously mentioned benefits of conservinglatent heat dissipation and conversion of evaporative heat transfer tosensible heating of the air are preserved. However, in this case, thevapor pressure of the initial stage fluid is never below that of theambient air, and moisture is not absorbed in the initial stage duringcooler nighttime temperatures as is the case when a desiccant fluid isused. Again, in any event, during operation of the entire heatdissipation system 100, the desiccant-based hygroscopic fluid of eachstage must remain stable (hygroscopic desiccant in solution) to preventcrystallization of the desiccant from the desiccant-based hygroscopicfluid.

Referring to drawing FIG. 11 , an alternative embodiment of a method andapparatus of the heat dissipation systems is described for supplementingthe water content of a liquid hygroscopic desiccant working fluid in aliquid hygroscopic desiccant-based heat dissipation system 200. In theheat dissipation system 200, the inherent osmotic gradient that existsbetween the liquid hygroscopic desiccant and a source ofdegraded-quality water is used to extract relatively pure water througha forward osmosis membrane 206 from the degraded source to the desiccantworking fluid. The water transferred by forward osmosis is of sufficientquality to prevent excessive accumulation of undesirable constituents inthe hygroscopic desiccant fluid circuit and, therefore, greatly expandsthe range of water quality that can be used to supplement the operationof a liquid hygroscopic desiccant-based heat dissipation system 200provided that the desiccant based hygroscopic fluid remains stable(hygroscopic desiccant in solution) to prevent crystallization of thedesiccant from the desiccant-based hygroscopic fluid.

Water added to the working fluid of the heat dissipation system 200provides several benefits to improve the performance of transferringheat to the atmosphere. First, the added water increases the moisturevapor pressure of the hygroscopic desiccant solution, which increasesthe proportion of latent cooling that can take place when the hothygroscopic desiccant is cooled by direct contact with ambient air. Thiseffectively increases the quantity of heat that can be dissipated perunit of desiccant-to-air contacting surface. Second, added water contentlowers the saturation temperature of the hygroscopic desiccant solution,which is the minimum temperature that the solution can be cooled to byevaporative cooling. By lowering the hygroscopic desiccant solution'ssaturation temperature, lower cooling temperatures can be achieved forotherwise equivalent atmospheric conditions. Third, water is generally asuperior heat-transfer fluid compared to the desiccant hygroscopicsolutions that would be employed in a heat dissipation system, such as200, and adding a higher proportion of it to the hygroscopic desiccantsolution will improve the hygroscopic desiccant solution's relevantthermal properties. In a desiccant-based heat dissipation system 200,the cool desiccant hygroscopic fluid is used to sensibly absorb heatfrom the thermal load in a heat exchanger, so it is preferred that thefluid have good heat-transfer properties. Water addition increases thedesiccant hygroscopic solution's specific heat capacity, and it reducesthe viscosity. Combined, these property improvements can lower theparasitic pumping load by reducing the needed solution flow rate for agiven heat load and by reducing the desiccant hygroscopic solution'sresistance to pumping.

In addition to improving the performance of a desiccant hygroscopicfluid heat dissipation system 200, the disclosed invention of the heatdissipation system 200 can also be viewed as an energy-efficient way toreduce the volume of a degraded water source that poses a difficultdisposal challenge. Forward osmosis is a highly selective process thatcan be used to separate water from a wide array of organic and inorganicimpurities found in degraded water sources, and when driven by theosmotic gradient between the water source and the desiccant in a heatdissipation system, it is also energy-efficient. Eliminating water inthis manner could be an integral part of water management for facilitieswith zero-liquid-discharge mandates.

As illustrated in drawing FIG. 11 , the alternative embodiment is aliquid desiccant-based heat dissipation system 200 coupled with aforward osmosis stage for supplementary water harvesting. Generaloperation of the heat dissipation system 200 includes circulating aliquid desiccant hygroscopic solution 201 through sensible heatexchanger 202 where it absorbs heat from the thermal load. Heateddesiccant hygroscopic solution is directly exposed to a flow of ambientair 203 in desiccant-to-air latent heat exchanger 204 where acombination of sensible heat transfer and latent heat transfer takesplace to cool the desiccant hygroscopic liquid so that it cancontinually transfer heat from the thermal load.

Supplementary water is added to the liquid desiccant solution through asecond circuit of desiccant hygroscopic solution 205 that flows alongone side of forward osmosis membrane 206. On the opposite side offorward osmosis membrane 206 is a flow of degraded quality water frominlet 207 to outlet 208 on one side of forward osmosis stage heatexchanger 206′. Since the osmotic pressure of the desiccant hygroscopicsolution 201 is higher than that of the degraded water source flowingthrough osmosis stage heat exchanger 206′, an osmotic pressure gradientis established that is used to transfer water 209 across forward osmosismembrane 206. Transferred water 209 becomes mixed with desiccanthygroscopic solution 201 and is used in the heat dissipation circuit.

Moisture in solution may also be extracted from the desiccanthygroscopic liquid in the form of liquid water when excess coolingcapacity is present. Drawing FIG. 12 illustrates an embodiment of theheat dissipation system of the present invention used in a steam-typepower system 300 including a desiccant evaporator 308 so that releasedvapor from the desiccant evaporator 308 meets the makeup water andcondenses directly in the plant's hygroscopic fluid-based heatdissipation system 310. The steam-type power system 300 includes aboiler 302 producing steam for a power turbine 304. Primary steamturbine exhaust 315 is routed to hygroscopic fluid-based heatdissipation system 310 for condensation back to boiler feed water. Asecondary steam exhaust flow is routed to sensible heat exchanger 306 toheat a slipstream of desiccant-based hygroscopic fluid before it entershygroscopic fluid vacuum evaporator 308. The desiccant evaporator 308includes a vacuum-type evaporator for evaporating the water fromdesiccant hygroscopic water from the sensible heat exchanger 306 for theevaporated water to be used as makeup water for the boiler with anyexcess water exiting the system 300 through excess water tap 314 forstorage for subsequent use in the system 300. Depending upon the type ofdesiccant hygroscopic liquid used in latent heat exchanger 310 which issubsequently evaporated by the desiccant hygroscopic evaporator 308, theamount of excess free water will vary from the desiccant hygroscopicevaporator 308 for use as makeup water for the system 300. However, inany event, during operation of the heat dissipation system, desiccantbased hygroscopic fluid must remain stable (hygroscopic desiccant insolution) to prevent crystallization of the desiccant from thedesiccant-based hygroscopic fluid.

In embodiments herein, where thermal energy and moisture are describedas being transferred between the hygroscopic working fluid and theambient atmosphere, such as in a fluid-air contactor, the presentinvention provides a corresponding embodiments wherein thermal energyand moisture are transferred between the hygroscopic working fluid and acooling gas composition, wherein the cooling gas composition can be anysuitable cooling gas composition. For example, the cooling gascomposition can include the ambient atmosphere, a gas having lessmoisture than the ambient atmosphere, a gas having more moisture thanthe ambient atmosphere, or a combination thereof.

Method of Cooling a Feed Gas.

In various embodiments, the present invention provides a method ofcooling a feed gas. The method includes any embodiment of a methoddescribed herein that includes a hygroscopic working fluid, whereinthermal energy is transferred from the feed gas to the hygroscopicworking fluid. In some embodiments, the thermal energy can betransferred directly, such as wherein the hygroscopic working fluid andthe feed gas both enter the same heat transfer device. In someembodiments, the thermal energy can be transferred indirectly, such aswherein one or more intermediate heat transfer media are used totransfer the thermal energy from the feed gas to the hygroscopic workingfluid.

The feed gas can be any suitable feed gas. The feed gas can include orcan be any suitable one or more gases. The feed gas can include theambient atmosphere, a gas having more water vapor than the ambientatmosphere, a gas having less water vapor than the ambient atmosphere,or a combination thereof. In some embodiments, the feed gas is theambient atmosphere. In some embodiments, the feed gas is taken from anenvironment in need of cooling, dehumidification, or a combinationthereof, and then returned thereto after being cooled by the method. Thefeed gas can include humidity from at least one of a spray, mist, or fogof water directly into the feed gas composition, an exhaust gas streamfrom a drying process, an exhaust gas stream consisting of high-humidityrejected air displaced during the ventilation of conditioned indoorspaces, an exhaust airstream from a wet evaporative cooling tower, andan exhaust flue gas stream from a combustion source.

The method can include using the cooled feed gas in any suitable way,such as using the cooled feed gas for HVAC applications, or feeding thecooled feed gas to a mechanical apparatus. The method can includefeeding the cooled feed gas to a rotary mechanical device, such as aturbine. In some embodiments, the turbine is a combustion turbine, suchas a natural gas combustion turbine. The turbine can be used to generateelectrical power. The cooled feed gas can allow the turbine to operatemore efficiently than the uncooled feed gas. The feed gas heat exchangerand the process heat exchanger can be parts of a turbine inlet chillingsystem (TIC).

In some examples, the method can include transferring thermal energyfrom the feed gas to a process fluid (e.g., via the feed gas heatexchanger, such as a chiller including a condenser, such as coolingcoils), and then transferring thermal energy from the process fluid tothe hygroscopic working fluid. The thermal energy can be transferreddirectly from the feed gas to the process fluid, without intermediateheat transfer media. The thermal energy can be transferred directly fromthe process fluid to the hygroscopic working fluid, or the thermalenergy can be transferred from the process fluid to a heat transfermedium (e.g., a chiller working fluid) and then from the heat transfermedium to the hygroscopic working fluid. Any suitable method oftransferring thermal energy from the feed gas to the process fluid canbe used, such as those described in U.S. RE 44,815 E1, herebyincorporated by reference in its entirety.

The method can include transferring thermal energy from a heated processfluid to the hygroscopic working fluid in a process heat exchanger, toform a cooled process fluid. The method can include transferring thermalenergy from the feed gas to the cooled process fluid in a feed gas heatexchanger, to form a cooled feed gas and the heated process fluid. Themethod can include dissipating thermal energy from the hygroscopicworking fluid to a cooling gas composition with a fluid-air contactor.The method can include transferring moisture between the hygroscopicworking fluid and the cooling gas composition with the fluid-aircontactor. The method can include adding at least part of the condensateto the hygroscopic working fluid. In some embodiments, the method caninclude feeding the cooled feed gas to a rotary mechanical device, suchas a turbine, such as a combustion turbine.

The process fluid can include any one or more suitable heat transfermedia. The process fluid can be a single phase (gas or liquid) thatrequires sensible cooling or it could be a two-phase fluid thatundergoes a phase change in the process heat exchanger, e.g.,condensation of a vapor into a liquid. The process fluid can includewater, calcium chloride brine, sodium chloride brine, an alcohol,ethylene glycol, a polyethylene glycol, propylene glycol, apolypropylene glycol, a mineral oil, a silicone oil, diphenyl oxide,biphenyl, an inorganic salt, a Therminol® brand heat-transfer fluid, aDowtherm™ brand heat-transfer fluid, a refrigerant (e.g., a fluorinatedhydrocarbon), or a combination thereof. Each one or more components ofthe process fluid can be any suitable weight percent of the processfluid, such as about 0.001 wt % to about 100 wt %, or about 0.01 wt % toabout 50 wt %, or about 0.001 wt % or less, or less than, equal to, orgreater than about 0.01 wt %, 0.1, 1, 2, 3, 4, 5, 6, 8, 10, 12, 14, 16,18, 20, 25, 30, 35, 40, 45, 50, 55, 60, 65, 70, 75, 80, 82, 84, 86, 88,90, 91, 92, 93, 94, 95, 96, 97, 98, 99, 99.9, 99.99, or about 99.999 wt% or more.

In some embodiments, cooling the feed gas can include condensing atleast some water out of the feed gas, to form a condensate. At leastpart of the condensate can be added to the hygroscopic working fluid. Insome embodiments, the method can provide sufficient condensate such thatthe amount of water lost from the hygroscopic fluid during the method(e.g., which can include or be limited to water lost from thehygroscopic working fluid to the cooling gas composition) is equal to orless than the amount of condensate produced, providing water-neutraloperation. For example, a rate of formation of the condensed liquid canbe equal to or greater than a rate than a rate of moisture mass transferbetween the hygroscopic working fluid and the cooling gas composition inthe fluid-air contactor. Over a period of time, such as 1 min or less,or less than, equal to, or greater than 30 min, 1 h, 2 h, 3, 4, 5, 6, 7,8, 9, 10, 12, 14, 16, 18, 20, 22, 24 h, 1.5 d, 2d, 3, 4, 5, 6, 8, 10,12, or about 14 days or more, the total amount of the condensategenerated by the method can be equal to or can exceed the total amountof water lost from the hygroscopic working fluid during the method.

The method can include transferring thermal energy from a heated processfluid to the hygroscopic working fluid in a process heat exchanger, toform a cooled process fluid. The method can include condensing liquidfrom a feed gas on a heat transfer surface of a feed gas heat exchangerin contact with the cooled process fluid, to form a cooled feed gas, aheated process fluid, and a condensate. The method can includedissipating thermal energy from the hygroscopic working fluid to acooling gas composition with a fluid-air contactor. The method caninclude transferring moisture between the hygroscopic working fluid andthe cooling gas composition with the fluid-air contactor. The method caninclude adding at least part of the condensate to the hygroscopicworking fluid.

The cooled process fluid can have a temperature that is at or below thedew point of the feed gas, such that the cooled process fluid can coolthe feed gas to a temperature wherein water vapor in the feed gascondenses into liquid water. The cooled process fluid can have asub-ambient temperature. The cooled process fluid can have a temperaturethat is about 1° C. to about 100° C. below the temperature of the feedgas (e.g., when the feed gas is ambient atmosphere, below the ambienttemperature), about 1° C. to about 50° C. below the temperature of thefeed gas, about 2° C. to about 20° C. below the temperature of the feedgas, or less than, equal to, or more than about 1° C. below thetemperature of the feed gas, about 2° C., 3, 4, 5, 6, 8, 10, 12, 14, 16,18, 20, 25, 30, 35, 40, 45, 50, 55, 60, 65, 70, 75, 80, 85, 90, 95, orabout 100° C. or more less than the temperature of the feed gas. Thecondensing of the liquid from the feed gas can include transferringthermal energy from the feed gas to the cooled process fluid.

The process heat exchanger (e.g., the heat exchanger that providestransfer of thermal energy between the process fluid and the hygroscopicworking fluid with or without one or more intermediate heat transfermedia) can be a chiller. The chiller can move thermal energy from theheated process fluid to the hygroscopic working fluid via a chillerworking fluid (e.g., an intermediate heat transfer medium between theheated process fluid and the hygroscopic working fluid). The chiller caninclude a condenser of a refrigeration cycle that occurs within thechiller. The chiller can include a compressor that compresses a chillerworking fluid prior to transferring thermal energy from the compressedchiller working fluid to the hygroscopic working fluid. The chiller cantransfer heat directly from the compressed chiller working fluid to thehygroscopic working fluid without any intermediate heat exchangers andwithout any intermediate heat transfer medium. The chiller can include avalve that allows the chiller working fluid to expand prior totransferring thermal energy from the heated process fluid to theexpanded chiller working fluid.

The chiller working fluid can include any one or more suitable heattransfer media. The chiller working fluid can be a single phase (gas orliquid) that requires sensible cooling or it can be a two-phase fluidthat undergoes a phase change in the chiller, e.g., a refrigerant thatundergoes condensation from a vapor (e.g., a gas) into a liquid and thenback to a vapor. The chiller working fluid can include water, calciumchloride brine, sodium chloride brine, an alcohol, ethylene glycol, apolyethylene glycol, propylene glycol, a polypropylene glycol, a mineraloil, a silicone oil, diphenyl oxide, biphenyl, an inorganic salt, aTherminol® brand heat-transfer fluid, a Dowtherm™ brand heat-transferfluid, a refrigerant (e.g., one or more of a fluorinated hydrocarbon, ahydrofluoroolefin, carbon dioxide, ammonia, and the like), an absorptionrefrigeration pair (e.g., one or more of ammonia-water, water-lithiumbromide, and the like), or a combination thereof. Each one or morecomponents of the chiller working fluid can be any suitable weightpercent of the chiller working fluid, such as about 0.001 wt % to about100 wt %, or about 0.01 wt % to about 50 wt %, or about 0.001 wt % orless, or less than, equal to, or greater than about 0.01 wt %, 0.1, 1,2, 3, 4, 5, 6, 8, 10, 12, 14, 16, 18, 20, 25, 30, 35, 40, 45, 50, 55,60, 65, 70, 75, 80, 82, 84, 86, 88, 90, 91, 92, 93, 94, 95, 96, 97, 98,99, 99.9, 99.99, or about 99.999 wt % or more.

The method can include transferring heat from the feed gas to the cooledprocess fluid immediately or shortly after forming the cooled processfluid without storing the cooled process fluid. The method can includestoring the cooled process fluid for a time period prior to transferringheat from the feed gas thereto, such as in a process fluid storage area(e.g., a tank, which can be insulated or uninsulated). The cooledprocess fluid can be stored for any suitable time prior to transferringheat thereto, such as about 1 minute to about 7 days, or about 1 min orless, or less than, equal to, or greater than 30 min, 1 h, 2 h, 3, 4, 5,6, 7, 8, 9, 10, 12, 14, 16, 18, 20, 22, 24 h, 1.5 d, 2d, 3, 4, 5, 6, 8,10, 12, or about 14 days or more.

The method can include adding at least some of the condensate to thehygroscopic working fluid immediately or shortly after forming thecondensate without storing the condensate. The method can includestoring the condensate for a time period prior to adding the condensateto the hygroscopic working fluid, such as in a condensate storage area(e.g, a tank). The condensate can be stored for any suitable time priorto adding a portion thereof to the hygroscopic working fluid, such asabout 1 minute to about 10 year, about 1 minute to about 7 days, orabout 1 min or less, or less than, equal to, or greater than 30 min, 1h, 2 h, 3, 4, 5, 6, 7, 8, 9, 10, 12, 14, 16, 18, 20, 22, 24 h, 1.5 d,2d, 3, 4, 5, 6, 8, 10, 12, 14 d, 1 month, 2, 4, 6, 8, 10, 12 months, 1.5years, 2, 3, 4, 5, 6, 7, 8, 9, or about 10 years or more.

The method can include maintaining the hygroscopic working fluid toprevent crystallization of the desiccant from the desiccant-basedhygroscopic working fluid. For example, the method can includemaintaining the hygroscopic working fluid at a sufficiently hightemperature, maintaining the wt % water of the hygroscopic working fluidat a sufficiently high level, or a combination thereof, to substantiallyavoid crystallization of the desiccant from the desiccant-basedhygroscopic working fluid.

The cooling gas composition can be any suitable cooling gas composition.In some embodiments, the cooling gas composition can include or can bethe ambient atmosphere. In various embodiments, the cooling gascomposition can include or can be the ambient atmosphere, a gas havingmore water vapor than the ambient atmosphere (e.g., humidified ambientair), a gas having less water vapor than the ambient atmosphere (e.g.,dehumidified ambient air), or a combination thereof. The gas having moreor less water vapor than the ambient atmosphere can include at least oneambient air into which water has been evaporated by misting or spraying,an exhaust stream from a drying process, an exhaust stream ofhigh-humidity air displaced during ventilation of conditioned indoorspaces, an exhaust stream from a wet evaporative cooling tower, and aflue gas stream from a combustion source and the associated flue gastreatment systems. In various embodiments, the cooling gas compositionincludes humidity from at least one of a spray, mist, or fog of waterdirectly into the cooling gas composition, an exhaust gas stream from adrying process, an exhaust gas stream consisting of high-humidityrejected air displaced during the ventilation of conditioned indoorspaces, an exhaust airstream from a wet evaporative cooling tower, andan exhaust flue gas stream from a combustion source.

In some embodiments, dissipating thermal energy from the hygroscopicworking fluid to the cooling gas composition includes dissipatingthermal energy from the hygroscopic working fluid to the ambientatmosphere using the fluid-air contactor and dissipating thermal energyfrom the hygroscopic working fluid to a gas having either less watervapor or more water vapor than the ambient atmosphere using thefluid-air contactor. In some embodiments, transferring moisture betweenthe hygroscopic working fluid and the cooling gas composition includestransferring moisture between the hygroscopic working fluid and theambient atmosphere using the fluid-air contactor and transferringbetween the hygroscopic working fluid and a gas having either less watervapor or more water vapor than the ambient atmosphere using thefluid-air contactor.

The hygroscopic working fluid can be any suitable hygroscopic workingfluid. The hygroscopic working fluid can be a low-volatility workingfluid (e.g., a working fluid having a boiling point equal to or greaterthan water). The hygroscopic working fluid can be an aqueous solution,e.g., including about 20 wt % to about 99.999 wt % water, or about 50 wt% to about 99 wt % water, or about 20 wt % or less, or less than, equalto, or more than about 22 wt % water, 24 wt %, 26, 28, 30, 32, 34, 36,38, 40, 42, 44, 46, 48, 50, 52, 54, 56, 58, 60, 62, 64, 66, 68, 70, 72,74, 76, 78, 80, 82, 84, 86, 88, 90, 91, 92, 93, 94, 95, 96, 97, 98, 99,99.9, 99.99, or about 99.999 wt % or more water. In various embodiments,the hygroscopic working fluid can include at least one of sodiumchloride (NaCl), calcium chloride (CaCl₂)), magnesium chloride (MgCl₂),lithium chloride (LiCl), lithium bromide (LiBr), zinc chloride (ZnCl₂),sulfuric acid (H₂SO₄), sodium hydroxide (NaOH), sodium sulfate (Na₂SO₄),potassium chloride (KCl), calcium nitrate (Ca[NO₃]₂), potassiumcarbonate (K₂CO₃), ammonium nitrate (NH₄NO₃), ethylene glycol,diethylene glycol, propylene glycol, triethylene glycol, and dipropyleneglycol. The concentration of any one or more of the preceding componentsin the hygroscopic working fluid can be about 0 wt % to about 80 wt %,or about 0.01 wt % to about 50 wt %, or about 0 wt %, or about 0.01 wt %or less, or less than, equal to, or more than about 0.1 wt %, 1, 2, 3,4, 5, 6, 7, 8, 9, 10, 12, 14, 16, 18, 20, 22, 24, 26, 28, 30, 35, 40,45, 50, 55, 60, 65, 70, 75 wt %, or about 80 wt % or more. In variousembodiments, the hygroscopic working fluid includes an aqueous solutionthat includes calcium chloride (CaCl₂)).

The fluid-air contactor can be any suitable fluid-air contactor, such asany suitable fluid-air contactor described herein. The method caninclude cooling the process heat exchanger by a flowing film of thehygroscopic working fluid enabling both sensible and latent heattransfer to occur the transferring of thermal energy from the heatedprocess fluid. The fluid-air contactor can operate in at least onerelative motion including countercurrent, cocurrent, or crossflowoperation. In some embodiments, the performance of the fluid-aircontactor can be enhanced by at least one of forced or induced draft ofthe cooling gas composition by a powered fan, natural convection airflowgenerated from buoyancy differences between heated and cooled air, andinduced flow of the cooling gas composition generated by the momentumtransfer of sprayed working fluid into the cooling gas composition.Transferring moisture between the hygroscopic working fluid and thecooling gas composition can include using a working fluid-air contactorand a vacuum evaporator. Transferring moisture between the hygroscopicworking fluid and the cooling gas composition can include the use of aforward osmosis membrane of a forward osmosis water extraction cell.

In various embodiments, the only water added to the hygroscopic workingfluid during the method is the condensate. In some embodiments, the heattransfer from the feed gas can be enhanced by addition of moisture tothe hygroscopic working fluid using at least one of: direct addition ofliquid water to the hygroscopic working fluid; absorption of relativelypure water directly into the hygroscopic fluid through the forwardosmosis membrane of a forward osmosis water extraction cell; absorptionof vapor-phase moisture by the working fluid from a moisture-containinggas stream outside of the process air contactor where themoisture-containing gas stream including at least one of ambient airinto which water has been evaporated by spraying or misting flue gasfrom a combustion source and its associated flue gas treatmentequipment; exhaust gas from a drying process; rejected high-humidity airdisplaced during ventilation of conditioned indoor air; and an exhaustairstream from a wet evaporative cooling tower. In some embodiments, theprocess heat exchanger is placed at the inlet to the fluid-air contactorfor raising humidity levels of the cooling gas composition. In someembodiments, the process heat exchanger is placed at the outlet of saidair contactor for lowering humidity of the cooling gas composition.

FIG. 13 illustrates an example of a system that can be used to performan embodiment of the method of cooling a feed gas, using desiccant-basedhygroscopic fluid cooling system 401 to meet the heat rejection needs ofTIC system 402. Sub-ambient cooling temperatures are generated byvapor-compression chiller 403 that cools a circulating flow of water (orother heat transfer fluid) to chill the ambient air entering combustionturbine 404 using heat exchanger 405. The chiller can include compressor415 and valve 420. Heat from chiller condenser 406 is removed anddissipated by the desiccant-based hygroscopic fluid cooling system.Because of the favorable operating conditions associated with TIC, aless corrosive desiccant such as CaCl₂) can be used to cool thecondenser directly using appropriate materials such as titanium, whichis an available option for these large chillers. This option negates theneed for an intermediate heat exchanger which improves performance byeliminating 3° to 4° C. from the overall temperature differentialbetween the condensing refrigerant and the ambient air dry bulbtemperature.

During operation of the TIC system, the turbine inlet ambient air streamis frequently cooled below its dew-point in heat exchanger 405 resultingin condensed moisture collection in basin 407. Under high humidityconditions where TIC is favored, this latent cooling load can exceed 50%of heat exchanger 5's total cooling load. The rate of condensed watercollection in this case would exceed 40% of the evaporative makeup waterrequirement for a conventional wet cooling tower used to cool thechiller's condenser. This rate is a substantial fraction of consumptivewater use but is insufficient to make TIC a water-neutral process usingconventional wet cooling. The condensed water is largely free ofdissolved scale-forming constituents and is highly suitable to be usedas supplemental water in a desiccant-based hygroscopic fluid coolingsystem using transfer line 408. Moisture addition to the desiccantworking fluid lowers the desiccant concentration and increases thelatent cooling potential of the direct contact air-desiccant process,409, resulting in better cooling performance that is manifested as lowercold desiccant temperatures for a constant cooling load or a highercooling capacity for a fixed set of desiccant temperatures.

The previous description assumes coincident operation of chiller 403 andoperation of heat exchanger 405, however, there are instances where theoperation of the chiller is decoupled from the need for inlet chillingby the use of a heat transfer fluid storage tank 410. This configurationallows the chiller to run at night or other off-peak periods when powerdemand is low. Ambient temperatures are also lower during these periodswhich aids condenser heat rejection to the atmosphere. When thermalstorage is used water condensate is not formed when the chiller is inoperation but instead comes when the stored cold fluid is used to chillthe incoming turbine air. This condensate can be directly mixed with thedesiccant working fluid and stored in the cooling system's basin 411until the chiller and desiccant cooling system are activated at a latertime, or it can be stored in tank 412 and metered into the desiccantworking fluid at times that are most beneficial for efficient coolingperformance.

System.

In various embodiments, the present invention provides a system for heatdissipation that includes a hygroscopic working fluid. The system can beany suitable system that can be used to perform any embodiment of themethod described herein.

In some embodiments, the system includes a process heat exchangerconfigured to transfer thermal energy from a heated process fluid to ahygroscopic working fluid to form a cooled process fluid. The system caninclude a feed gas heat exchanger configured to condense liquid from afeed gas on a heat transfer surface of the feed gas heat exchanger incontact with the cooled process fluid, to form a cooled feed gas and acondensate. The system can include a fluid-air contactor configured todissipate heat from the hygroscopic working fluid to a cooling gascomposition, and configured to transfer moisture between the hygroscopicworking fluid and the cooling gas composition. The system can beconfigured to add at least part of the condensate to the hygroscopicworking fluid.

The feed gas heat exchanger and the process heat exchanger can be partsof a turbine inlet chilling system (TIC), such as for a natural gascombustion turbine. The system can be configured to operate in at leastwater-neutral operation with respect to moisture loss from thehygroscopic working fluid and moisture gain from the condensate. Thesystem can be configured to maintain the hygroscopic working fluid toprevent crystallization of the desiccant from the desiccant-basedhygroscopic working fluid.

The process heat exchanger can include or can be a chiller that movesthermal energy from the heated process fluid to the hygroscopic workingfluid via a chiller working fluid. The process heat exchanger caninclude a condenser of a refrigeration cycle. For example, the processheat exchanger can include the condenser of a chiller that rejectsthermal energy from the heated process fluid to the hygroscopic workingfluid via the chiller's refrigeration circuit. The chiller can include acompressor that is configured to compress a chiller working fluid priorto transferring thermal energy from the compressed chiller working fluidto the hygroscopic working fluid. The chiller can be configured totransfer heat directly from the compressed chiller working fluid to thehygroscopic working fluid without any intermediate heat exchangers andwithout any intermediate heat transfer medium. The chiller can include avalve that is configured to allow the chiller working fluid to expandprior to transferring thermal energy from the heated process fluid tothe expanded chiller working fluid.

The system can include a process fluid storage area configured to storethe cooled process fluid for a period of time before placing the cooledprocess fluid in the feed gas heat exchanger. The system can include acondensate storage area configured to store the condensate for a periodof time before placing at least a portion of the condensation in thehygroscopic working fluid.

Methods and Systems for Integrating Waste Water into Hygroscopic CoolingSystem and for Disposal of Waste Water.

In various embodiments, the present invention also provides a method ofusing waste water as makeup water in a hygroscopic cooling method. Useof waste water as makeup water for a hygroscopic working fluid isenvisaged for any embodiment of a method described herein that includesa hygroscopic working fluid.

In various embodiments, the present invention provides a system forusing waste water as makeup water in a hygroscopic cooling system. Useof waste water as makeup water for a hygroscopic working fluid isenvisaged for any embodiment of a system described herein that includesa hygroscopic working fluid. The system can be any suitable system thatcan be used to perform any embodiment of the method described herein.

In various embodiments, the present invention also provides a method ofdisposing of waste water, such as water treatment effluent, concentratedsalt stream and blowdown stream fluid, by adapting a hygroscopic coolingmethod to incorporate the waste water as makeup water. Any embodiment ofa method described herein that includes a hygroscopic working fluid maybe adapted to use waste water.

In various embodiments, the present invention provides a system fordisposing of waste water, such as water treatment effluent, concentratedsalt stream and blowdown stream fluid, by adapting a hygroscopic coolingsystem to accept the waste water as water makeup. Any embodiment of asystem described herein that includes a hygroscopic working fluid may beadapted to use waste water. The system can be any suitable system thatcan be used to perform any embodiment of the method described herein.

The method may comprise contacting a hygroscopic working fluid with aheat exchanger having a heated process fluid; transferring thermalenergy from the heated process fluid to the hygroscopic working fluidand flowing the resulting hygroscopic working fluid from the heatexchanger to a fluid-air contactor having an air stream; contacting thehygroscopic working fluid with the air stream of the fluid-aircontactor; transferring water from the hygroscopic working fluid to theair stream, collecting the resulting hygroscopic working fluid andcirculating it to the process heat exchanger; directing at least aportion of the hygroscopic working fluid to form a mixture with wastewater in a makeup mix tank at conditions to precipitate dissolvedimpurities from the mixture; and filtering the precipitate from themixture to form a filtrate and then directing the filtrate to combinewith the circulating hygroscopic working fluid; wherein the hygroscopicworking fluid comprises a desiccant and water. In various embodiments,the method may be for, but is not limited to, use in disposing of wastewater, use in maintaining the water content of hygroscopic workingfluid, use in cooling a process fluid, or any other purpose describedherein for a method comprising a hygroscopic working fluid.

The system may comprise a hygroscopic working fluid comprising adesiccant and water; a heat exchanger configured to transfer thermalenergy from a heated process fluid to the hygroscopic working fluid; afluid-air contactor having an air stream, wherein the fluid-aircontactor and air-stream are configured to transfer water from thehygroscopic working fluid to the air stream; wherein the heat exchangerand the fluid-air contactor are configured so the hygroscopic workingfluid is circulated through the heat exchanger and the fluid-aircontactor; a makeup mix tank configured to receive waste water and atleast some of the circulated hygroscopic working fluid, wherein themakeup mix tank is at conditions which permit the waste water and thehygroscopic working fluid to mix and to precipitate dissolved impuritiesfrom the resulting mixture; and a filter unit configured to removeprecipitated impurities from the mixture of waste water and hygroscopicworking fluid and direct the resulting filtrate to combine with thecirculated hygroscopic working fluid.

In various embodiments, the waste water may be, but is not limited to,blowdown from conventional cooling towers, water treatment effluent,waste scrubbing liquor from industrial processes, concentrated saltstream from a desalination process or concentrated reject from reverseosmosis treatment. Thus, in various embodiments, the hygroscopic coolingsystem is adapted to use various waste water streams as makeup waterinstead of using higher-quality water sources that would normally berequired for evaporative cooling makeup. The system can use a reducedamount of higher-quality water in comparison to what would be consumedwithout using waste water to provide cooling.

Waste water may be water which is not suitable for use in aconventional, non-hygroscopic cooling system.

Waste water may be brackish water, salt water, or more highlyconcentrated than brackish water or salt water. Waste water may includeconcentrate approaching its saturation limit. Waste water may benon-potable water which is contaminated with dissolved impurities. Wastewater may be water which has dissolved impurities susceptible toprecipitation or equipment fouling. Waste water may be aqueous wasteeffluent from a desalination process, reverse osmosis process, watertreatment process, an industrial process, power generation process,refrigeration process, industrial cleaning process, or cooling process.

In various embodiments, the water component of the waste water streammay be completely evaporated after incorporation and cycling in thehygroscopic cooling system. The dissolved solid component of the wastewater stream may be precipitated and filtered out and disposed oftogether with the tower's typical loading of captured airborne dust.

Although in various aspects, the present invention may emphasize waterconservation, e.g., conservation of high-quality water, and emphasizeminimizing evaporation of water in the hygroscopic fluid, the presentinvention may also emphasize maximizing evaporation of the water in thehygroscopic fluid, e.g., where waste water is incorporated into thehygroscopic fluid for the purpose of disposal.

In various embodiments, waste water can be a suitable weight percent ofthe makeup water, such as about 0.001 wt % to about 100 wt %, or about0.01 wt % to about 50 wt %, or about 0.001 wt % or less, or less than,equal to, or greater than about 0.01 wt %, 0.1, 1, 2, 3, 4, 5, 6, 8, 10,12, 14, 16, 18, 20, 25, 30, 35, 40, 45, 50, 55, 60, 65, 70, 75, 80, 82,84, 86, 88, 90, 91, 92, 93, 94, 95, 96, 97, 98, 99, 99.9, 99.99, orabout 99.999 wt % or more. The makeup water can be 100 wt % waste wateror it may be less than 100 wt % waste water.

The system may use low temperature waste heat resources to drive wastewater evaporation.

In various embodiments, use of the system and method of the presentinvention may solve a problem of waste water disposal.

A hygroscopic cooling system of the present invention may use wastewater as makeup water and dispose of it via evaporation to achieve zeroor near-zero liquid discharge requirements. For example, zero liquiddischarge requirements may be achieved by completely evaporating thewater portion of the makeup stream while precipitating any dissolvedsolids as filterable particulates. Energy to drive the process can comefrom low grade waste heat that would otherwise be dissipated in aconventional cooling tower. By making use of waste water resources toprovide cooling, the process and system reduces the amount ofhigher-quality water sources demanded, and may also lead to a netreduction in overall makeup water needed. In various embodiments, thepresent invention has the benefit of achieving zero liquid dischargewithout use of evaporation ponds or thermal treatment processes such asa brine crystallizer. Zero liquid discharge may be achieved in thecontext of the hygroscopic cooling system itself, or the context of thehygroscopic cooling system in connection with another system, e.g., adesalination system, reverse osmosis system, or conventional coolingsystem, to which the hygroscopic cooling system is attached. Thehygroscopic cooling system may be a means by which the desalinationsystem, reverse osmosis system, or conventional cooling system mayreduce or eliminate its discharge.

This invention can offer greater energy efficiency or cooling efficiencythan process cooling without waste water evaporation, or waste waterevaporation without process cooling. The invention can offer greaterefficiency and other advantages over a separate process cooling systemand waste water evaporation system that are not integrated.

Waste water cannot be suitably used for conventional cooling towermakeup water due to dissolved impurities. Such impurities can causechemical and physical deterioration of the conventional cooling processsystem. Subsequent precipitation of impurities in the cooling system cancause equipment fouling and reduced performance of the system. Moreover,a problem arises if waste water is used in a conventional, evaporativecooling system because precipitation can occur in unpredictable orundesirable locations. For example, precipitation may occur whereconcentration builds, e.g., as water evaporates, and precipitation mayoccur at temperature gradients, e.g., in the heat exchanger or on thetower's wetted fill.

However, when waste water is suitably used as described herein as makeupwater for a hygroscopic working fluid, the hygroscopic working fluid canbe mixed with the makeup stream in a manner to induce precipitation of awide range of dissolved impurities upon mixture with the makeup stream.In various embodiments, properties of the hygroscopic working fluid aresuch that it will preferentially force the precipitation of a wide rangeof dissolved impurities when mixed with the makeup stream. In variousembodiments, the precipitate results in suspended particulates which aresubsequently filtered out.

In various embodiments, the hygroscopic working fluid and waste waterare mixed and impurities are precipitated in a makeup mix tank for whichconditions and component amounts can be separately controlled from otherparts of the hygroscopic cooling system.

By controlling the location, temperature, and duration of the mixingprocess, precipitation of dissolved solids can be conducted undercontrolled conditions to result in filterable suspended particulatesthat do not lead to equipment fouling. As discussed herein, ifcontinuous evaporation of water with high dissolved solids content wereattempted in a conventional cooling tower, the system's heat exchangesurfaces would rapidly become fouled from scale formation since theselocations correspond to solubility changes associated with temperaturegradients. In contrast, in various embodiments of the hygroscopiccooling system of the present invention, a sharp change in solubilityoccurs at the makeup fluid mix tank due to an increase in the totaldissolved solids concentration and this sharp change in solubilityresults in controlled precipitation. In various embodiments, waste wateris mixed with hygroscopic working fluid at a temperature and duration toinduce precipitation of dissolved solid impurities, such as about 0.001wt % to about 100 wt %, or about 0.01 wt % to about 50 wt %, or about0.001 wt % or less, or less than, equal to, or greater than about 0.01wt %, 0.1, 1, 2, 3, 4, 5, 6, 8, 10, 12, 14, 16, 18, 20, 25, 30, 35, 40,45, 50, 55, 60, 65, 70, 75, 80, 82, 84, 86, 88, 90, 91, 92, 93, 94, 95,96, 97, 98, 99, 99.9, 99.99, or about 99.999 wt % or more of thedissolved impurities based on the total weight of dissolved soldimpurities.

In various embodiments, yet without being limited by theory, the processby which dissolved solids are precipitated in the presence of adesiccant is according to a solubility equilibrium and thus is generallyunaffected by changes to the particular makeup of the dissolved solids.

In various embodiments, the desiccant mass concentration (mass ofdesiccant/volume of mixture) in the mixture of hygroscopic working fluidand waste water, in the makeup mix tank is 0.001% to about 80%, or about0.01 wt % to about 50 wt %, or about 0.001 wt % or less, or less than,equal to, or greater than about 0.01 wt %, 0.1, 1, 2, 3, 4, 5, 6, 8, 10,12, 13, 14, 15, 16, 18, 20, 25, 30, 35, 40, 45, 50, 55, 60, 65, 70, 75,or about 80 wt %. In various embodiments, desiccant mass concentrationis at least about 5%. In various embodiments, desiccant massconcentration is greater than 5%. In various embodiments, desiccant massconcentration is at least about 15%. In various further embodiments,desiccant mass concentration is greater than 15%. In various furtherembodiments, desiccant mass concentration is greater than 30%.

In various embodiments, the mixture of hygroscopic working fluid andwaste water in the makeup mix tank is at a temperature suitable forprecipitation of dissolved solid impurities, which may be from justabout the freezing point of the mixture to just under the boiling pointof the mixture. The temperature may be 0.1° C. to about 90° C., or about5° C. to about 50° C., or about 10° C. to about 30° C., about roomtemperature, less than about room temperature, or greater than aboutroom temperature, or less than, equal to, or greater than about 0.1, 1,2, 3, 4, 5, 6, 8, 10, 12, 14, 16, 18, 20, 25, 30, 35, 40, 45, 50, 55,60, 65, 70, 75, 80, 82, 84, 86, 88, or 90° C.

In various embodiments, the mixture of hygroscopic working fluid andwaste water in the makeup mix tank is permitted to linger for a periodof time sufficient to permit precipitation of the desired amount ofdissolved solid impurities. Precipitation time may be controlled bymanaging the size of the makeup mix tank and adjusting the inlets andoutlets of the makeup mix tank.

In various embodiments, the mixture of hygroscopic working fluid andwaste water in the makeup mix tank is such that the makeup mix tank isgently mixed to avoid agitating the mixture in such a way as to hinderprecipitation. In various embodiments, the makeup mix tank constitutes aplurality of tanks. In various embodiments, the makeup mix tank maycontain a mixing tank and a precipitation tank. In various embodiments,the makeup mix tank achieves precipitation by establishing a sharpconcentration or temperature gradient.

FIG. 14 illustrates one example of a system that can be used for bothheat dissipation and disposal of waste water. The waste water may bewaste water or blowdown stream fluid produced from a conventionalcooling system, such as those used for power plants or other industrialprocess. A hygroscopic cooling system 500 is integrated with aconventional cooling system 501 and the hygroscopic cooling system isused to dispose of the blowdown stream 502 of the primary cooling tower504 of the conventional cooling system.

Referring to FIG. 14 , a process fluid enters through hot-side inlet 505through a turbine 506 and a steam condenser or other process heatexchanger 507 which is cooled via conventional cooling and exits throughhot-side outlet 508. The conventional cooling system includes aconventional cooling fluid which is routed through a pump 509, to a heatexchanger 507 configured to cool the process fluid by removing thermalenergy from the process fluid to the conventional cooling fluid, furtherto a heat exchanger 510 configured to cool the conventional coolingfluid by removing thermal energy from the conventional cooling fluid tothe hygroscopic working fluid, and then to distribution nozzles 511which spray the conventional cooling fluid into contact with air in theprimary cooling tower 504, and the conventional cooling fluid iscollected in a reservoir 512 or into a blowdown stream collection inlet513. A water makeup 514 provides water of suitably high quality, e.g.,fresh water, to the reservoir or adjacent portion of the conventionalcooling system. The blowdown stream collection inlet routes thecollected fluid, which is blowdown stream fluid, via a blowdown stream502 from the conventional cooling system to a makeup mix tank 515 inwhich the blowdown stream fluid is mixed with hygroscopic working fluid.The makeup mix tank stream 515 is configured to accept a suitable amountof hygroscopic working fluid and blowdown stream fluid under conditionsto precipitate impurities incorporated into the mixture from theblowdown stream fluid or elsewhere. In various embodiments, heatexchanger 507 may be a steam condenser. In various embodiments, heatexchanger 510 may be a steam condenser.

Referring further to FIG. 14 , The hygroscopic cooling system includes ahygroscopic working fluid which is mixed with a waste water, e.g., theblowdown stream fluid, at a makeup mix tank 515. The mixture is inducedto precipitate particles of impurities which have become incorporatedinto the mixture. The resulting mixture routed through a filter 516 tocollect precipitate solids and atmospheric particles from the mixture,which may be removed by cleaning or replacing the filter or via a solidwaste disposal mechanism 521. The filtered fluid is then routed theremainder of the hygroscopic cooling system. The hygroscopic coolingsystem further includes a reservoir 517, one or more pumps 518, the heatexchanger 510 configured to cool the conventional cooling fluid byremoving thermal energy from the conventional cooling fluid to thehygroscopic working fluid, distribution nozzles 519 which spray thehygroscopic working fluid into contact with air in the hygroscopiccooling tower 503 which is collected in the reservoir 517. Thehygroscopic cooling system further includes a valve 520, which iscontrolled to provide a suitable amount of hygroscopic working fluid tothe makeup mix tank 515 to control or induce precipitation of impuritiesprior to transfer to the filter 515.

Thus, in various embodiments, the makeup mix tank 515 provides a makeupfluid to the hygroscopic working fluid. The makeup fluid may be derivedfrom waste water, such as blowdown stream fluid.

It is envisaged that the conventional cooling tower may be substitutedwith other forms of conventional fluid-air contactor.

It is also envisaged that the hygroscopic cooling tower may besubstituted with other forms of hygroscopic fluid-air contactor.

The system of FIG. 14 can represent, generically, any of the hygroscopiccooling systems described in this document, adapted to integrate aconventional cooling system or power plant, and accept waste watertherefrom.

In various embodiments, a power plant is integrated with a hygroscopiccooling tower to process the blowdown stream from a conventional plantcooling tower. The primary tower's blowdown stream may be completelyevaporated to provide cooling and dissolved contaminants areprecipitated as filterable solids.

FIG. 15 illustrates another example of a system that can be used forboth heat dissipation and disposal of waste water. The waste water maybe a concentrated salt stream produced from a desalination system. Ahygroscopic cooling system 500, demarked by the dotted line, isintegrated with a desalination system 522, and the hygroscopic coolingsystem is used to dispose of the concentrated salt stream 523 producedfrom the desalination system 522.

Referring to FIG. 15 , a desalination system having a brackish waterintake 524 which transfers brackish water into the desalination systemwhich produces a desalinated effluent 525 and a concentrated salt stream523. The concentrated salt stream is routed to a makeup mix tank 515 inwhich the concentrated salt stream is mixed with hygroscopic workingfluid. The makeup mix tank stream 515 is configured to accept a suitableamount of hygroscopic working fluid and concentrated salt stream underconditions to precipitate impurities incorporated into the mixture fromthe concentrated salt stream or elsewhere.

Referring further to FIG. 15 , the hygroscopic cooling system 500includes a hygroscopic working fluid which is mixed with a waste water,e.g., the concentrated salt stream, at a makeup mix tank 515. Themixture is induced to precipitate particles of impurities which havebecome incorporated into the mixture. The resulting mixture routedthrough a filter 516 to collect precipitate solids and atmosphericparticles from the mixture, which may be removed by cleaning orreplacing the filter or via a solid waste disposal mechanism 521. Thefiltered fluid is then routed the remainder of the hygroscopic coolingsystem. The hygroscopic cooling system further includes a reservoir 517,one or more pumps 518, a heat exchanger 510 configured to remove thermalenergy from a hot external working fluid or process fluid, distributionnozzles 519 which spray the hygroscopic working fluid into contact withair in the hygroscopic cooling tower 503 which is collected in thereservoir 517. The hygroscopic cooling system further includes a valve520, which is controlled to provide a suitable amount of hygroscopicworking fluid to the makeup mix tank 515 to control or induceprecipitation of impurities prior to transfer to the filter 515. Thus,in various embodiments, the makeup mix tank 515 provides a makeup fluidto the hygroscopic working fluid. The makeup fluid may thus be derivedfrom waste water produced by a desalination system, including aconcentrated salt stream.

Referring yet further to FIG. 15 , a hot external working fluid orprocess fluid enters through hot-side inlet 526 through a heat exchanger510 configured to removing thermal energy from the working fluid orprocess fluid to the hygroscopic working fluid. The hot external workingfluid or process fluid may be part of a cooling system for a powerplant,part of a cooling system for a desalination plant, part of a coolingsystem for a refrigeration unit, or part of a cooling system for anair-conditioning unit. In various embodiments, heat exchanger 510 may bea steam condenser.

In various embodiments, the hygroscopic cooling system and desalinationsystem may be separate facilities. In other embodiments, the hygroscopiccooling system and desalination system are the same facility.

It is envisaged that the hygroscopic cooling tower may be substitutedwith other forms of hygroscopic fluid-air contactor.

The system of FIG. 15 can represent, generically, any of the hygroscopiccooling systems described in this document, adapted to integrate adesalination system, or other system which produces a concentrated saltstream, and accept waste water therefrom.

FIG. 16 illustrates another example of a system that can be used forboth heat dissipation and disposal of waste water. The waste water maybe a reverse osmosis concentrate produced from a reverse osmosis system,e.g., a desalination system or a water treatment system. A hygroscopiccooling system 600 is integrated with a reverse osmosis system 601 andthe hygroscopic cooling system is used to dispose of the reverse osmosisconcentrate 603 produced from the reverse osmosis system.

Referring to FIG. 16 , a reverse osmosis system has a brackish or wastewater feed 604 which is processed to produce a reverse osmosis permeate605 and a reverse osmosis concentrate 603. The reverse osmosisconcentrate is routed to a makeup mix tank 606 in which the reverseosmosis concentrate is mixed with hygroscopic working fluid in a makeupwater circuit 607. The makeup water mix tank stream 606 is configured toaccept a suitable amount of hygroscopic working fluid and reverseosmosis concentrate under conditions to precipitate impuritiesincorporated into the mixture from the concentrated salt stream orelsewhere. The makeup water circuit includes hygroscopic working fluid,one or more pump 608, a filter 609, a makeup mix tank 606 hygroscopicworking fluid, and a portion of the makeup water circuit that overlapswith the hygroscopic cooling circuit 615, e.g., via reservoir 610. Thus,the makeup water circuit accepts fluid from the hygroscopic coolingcircuit and provides makeup fluid to the hygroscopic cooling circuit.The hygroscopic working fluid is mixed with waste water, e.g., thereverse osmosis concentrate, at makeup mix tank 606. The mixture ofhygroscopic working fluid and waste water is induced to precipitateparticles of impurities which have become incorporated into the mixture.The resulting mixture is routed through a filter 609 to collectprecipitate solids and atmospheric particles from the mixture, which maybe subsequent removed by cleaning or replacing the filter or via a solidwaste disposal mechanism 616. The filtered fluid is then routed to theremainder of the hygroscopic cooling system via, e.g., transfer into thereservoir 610 which is configured to circulate back to the makeup mixtank 606.

Referring further to FIG. 16 , the hygroscopic cooling system furtherincludes a hygroscopic cooling circuit having a hygroscopic coolingtower 611, a reservoir 610, one or more pumps 612, a heat exchanger 613which is configured to remove thermal energy from a hot external workingfluid or process fluid, and distribution nozzles 614 which spray thehygroscopic working fluid into contact with air in the hygroscopiccooling tower 611 which is collected in the reservoir 610. In variousembodiments, the hygroscopic cooling system further includes a valve,which is controlled to provide a suitable amount of hygroscopic workingfluid from the reservoir 610 to the makeup mix tank 606 to control orinduce precipitation of impurities prior to transfer to the filter 609.In various embodiments, heat exchanger 613 may be a steam condenser.Thus, in various embodiments, the makeup mix tank 606 provides a makeupfluid to the hygroscopic working fluid. The makeup fluid may thus bederived from waste water produced by a desalination system, including aconcentrated salt stream.

It is envisaged that the hygroscopic cooling tower may also besubstituted with other forms of hygroscopic fluid-air contactor.

The system of FIG. 16 can represent, generically, any of the hygroscopiccooling systems described in this document, adapted to integrate areverse osmosis system, or any other system which produces a reverseosmosis stream, and accept waste water therefrom.

In various embodiments, the hygroscopic cooling system and reverseosmosis system may be separate facilities. In other embodiments, thehygroscopic cooling system and reverse osmosis system are the samefacility.

In various embodiments, the hygroscopic cooling is integrated with afirst reverse osmosis process and a second reverse osmosis process,which may be configured in series or in parallel. For example, a firstreverse osmosis process may be softening and the second reverse osmosisprocess may be salt water reverse osmosis.

In various embodiments, where hygroscopic working fluid is mixed withwaste water it is mixed in a settling chamber. Thus, a makeup mix tankmay be a settling chamber. In various embodiments, the settling chamberhas a slipstream of the circulating desiccant solution. In variousembodiments, the waste water and hygroscopic working fluid are permittedto reach equilibrium. After equilibrium, excess dissolved solids canprecipitate from solution and can be filtered from the liquid along withthe normal loading of fine airborne particles that are typicallyscrubbed from the air via the cooling towers. The collected solids maybe disposed of through conventional means while the liquid returns tothe hygroscopic cooling tower and the added water is used to sustainevaporative cooling of the hygroscopic cooling system.

In various embodiments, when makeup fluid for the hygroscopic workingfluid is derived from waste water it is not necessary that water savingsbe emphasized, and instead the hygroscopic properties of the desiccantmay be used to completely absorb water from the effluent stream,precipitating and removing the dissolved solid impurities, andevaporating the water. In various other embodiments, only as much waterfrom the effluent stream is used so as to maintain the hygroscopiccooling system.

The waste water may be transferred via a conduit, e.g., piping, from onefacility which generates the waste water to another facility that hasthe hygroscopic cooling system which accepts the waste water. Forexample, various embodiments may include a host site having ahygroscopic cooling system and an external site which provides the wastewater to the hygroscopic cooling system.

The host site may be an electric power plant. The host site may be aplant using a steam Rankine cycle for power generation, e.g., nuclear,coal, or natural gas combined cycle. The host site may be a power planthaving from 500 MWe to 1000 MWe generating capacity. The host site mayalso be a specialized commercial cooling operation, such as refrigeratedwarehouses, distribution centers and data centers. The host site may belarge air-conditioning systems, such as found in hospitals, schoolcampuses, or other facilities with a large centralized cooling system,particularly those that are wet-cooled using cooling towers. In variousembodiments, the host site operates year-round.

In various embodiments, in the hygroscopic cooling tower, heat isdissipated to the atmosphere much like it is in a conventional coolingtower except that the coolant is a concentrated desiccant solution thatis used to regulate the amount of evaporative heat transfer. Thiscontrol allows for water savings which is one advantage of hygroscopiccooling, but incorporation of waste water as makeup water provides anadditional or alternative use, wherein a desired amount of water isevaporated, e.g., the amount of water from a conventional coolingtower's blowdown stream or the amount of water in a concentrated saltstream from a desalination system, is completely evaporated to providecooling and dissolved contaminants are precipitated as filterablesolids.

Thus, in various embodiments, the hygroscopic cooling system functionsas an environmentally-friendly means to dispose of water obtained viaaddition of waste water to the hygroscopic cooling system.

EXAMPLES

Various embodiments of the present invention can be better understood byreference to the following Examples which are offered by way ofillustration. The present invention is not limited to the Examples givenherein.

Examples 1 and 2 are performance models based on experiments that wereperformed.

Example 1

In this Example, a TIC system operates at a ambient design point valueof 95° F. (35° C.) dry bulb temperature and a corresponding 75° F. (24°C.) wet bulb temperature. The chilling system cools the incoming ambientair to 50° F. (10° C.) in order to benefit the operating performance ofthe combustion turbine of a natural gas combined cycle power plant.Approximately 55 MW (thermal) of cooling is required for thisapplication, 37% of which is used for condensing water out of the air(latent cooling load), and the remainder is used to sensibly cool theremaining air. The resulting condensate is collected at a rate of 135gpm (8.55 kg/s). Under these conditions the condenser of the TIC mustreject approximately 65 MW (thermal) to the ambient environment. If awet evaporative cooling system were used, it would consume 453 gpm (28.6kg/s) of water to makeup evaporation losses assuming a system designedto achieve a condenser temperature of 108° F. (42° C.).

Under daytime operation a desiccant-based cooling system designed for a40° F. (22° C.) temperature difference between the ambient dry bulbtemperature and that of the condenser would consume no water, but wouldresult in a higher condenser temperature of 135° F. (57° C.). However,by consuming the condensate from the air chilling process, the condensertemperature could be reduced by 7° F. (4° C.) with no other changes tothe cooling system's size or air flow. This improvement in performancerepresents the equivalent of increasing the size of a totally drycooling system by 22%, which can be completely avoided by making use ofthe TIC system's own produced water.

Example 2

If instead thermal storage is used to provide inlet air chilling duringthe day, the same quantity of condensate would be collected but theoperation of the cooling system would be deferred to the coolernighttime hours. Assuming a 78° F. dry bulb temperature and a 75° F. wetbulb temperature, the same size desiccant-based system as used inExample 1 could cool the condenser to 117° F. (47° C.) in a completelydry mode with no water consumption. Alternatively, if the condensatecollected during the day were consumed as evaporative makeup in the samecooling system, the resulting condenser temperature would be 109° F.(42.8° C.), nearly equaling the cooling performance of a wet system butby using only the collected condensate as makeup.

The foregoing discussion discloses and describes merely exemplaryembodiments of the present invention. One skilled in the art willreadily recognize from such discussion, and from the accompanyingdrawings and claims, that various changes, modifications, and variationscan be made therein without departing from the spirit and scope of theinvention as defined in the following claims.

Example 3

The effect of the hygroscopic working fluid desiccant concentration onthe dissolved solids solubility was analyzed. Three samples of reverseosmosis concentrate were evaluated to identify species withprecipitation potential. The three samples are summarized in Table 1.

TABLE 1 Reverse Osmosis (RO) Samples 1-3. Sample 1 Sample 2 Sample 3 RORecovery 70% 75% 82.5% Source RO Source RO Source RO Water Quality FeedConcentrate Feed Concentrate Feed Concentrate Parameters (mg/L) (mg/L)(mg/L) (mg/L) (mg/L) (mg/L) Calcium 445 1476 270 1079 147 718 Magnesium235 780 60 260.6 38 199 Potassium 3.1 10.2 7 25.7 17 74 Sodium 470 1820250 774 711 3327 Bicarbonate 200 798 218 809 78 379 Chloride 655 2351790 2953 1267 6271 Sulfate 2000 6635 136 489 307 1493 SiO₂ 21.5 71 44154 31 201 TDS 3940 13979 1820 6652 2665 13039 pH 7.51 7.05 7.5 7.7 7.77.9 Temp (° C.) 20.9 21 22 22 26 26

PHREEQC Interactive (Version 3.310.12220) software from the UnitedStates Geological Survey was used to calculate saturation index valuesfor species in each of the samples and the results are summarized inTable 2 and FIG. 17 .

TABLE 2 Positive Saturation Index Values Calculated For Samples 1-3.Sample 1 Sample 2 Sample 3 Talc 0.8 1.45 0.85 Quartz 0.74 1.13 1.14Magnesite 0.1 Huntite 0.19 Gypsum 0.45 Dolomite 1.62 1.73 0.67Chalcedony 0.31 0.7 0.71 Calcite 0.77 1.04 0.46 Aragonite 0.48 0.76 0.18Anhydrite 0.11

The data show precipitation potential of key species includingcalcium-based carbonates and sulfates, along with silica. For example,FIG. 17 and Table 2 show data for talc, which is representative ofsilicates; quartz and chalcedony, which is representative of silica;gypsum, which is representative of calcium sulfates, dolomite, which isrepresentative of calcium-magnesium carbonates; and calcite andaragonite, which is representative of calcium carbonates. PHREEQCsoftware was further used to compute the maximum solubility of thesespecies in the presence of the desiccant at various concentrationlevels; these results are summarized in FIGS. 18A, 18B, 18C and 18D. Foreffective control over water savings, the desiccant concentration in ahygroscopic cooling system will generally be about 15% by mass of thehygroscopic fluid. According to the results shown in FIG. 18A-C, themaximum solubility for CaCO₃, CaSO₄ and SiO₂ at this concentration isless than half that estimated with no desiccant (0%) which is the sourceof the sharp gradient needed to initiate precipitation. Highly solublespecies in the reverse osmosis concentrate such as NaCl do not undergoas dramatic a decrease in solubility as do the sparingly soluble speciesshown in FIG. 18D. However, such highly soluble species can also beforced from solution by concentrating the desiccant in order to maintainthe dissolved mineral balance. This can be understood analogously to howthe purity of brine solutions is industrially increased from naturallyoccurring sources of brine solution. As discussed herein, without beinglimited to theory, the process by which dissolved solids areprecipitated in the presence of a desiccant may exhibit an equilibriumphenomenon which is unaffected by changes to the makeup of the dissolvedsolids. Each of the three reverse osmosis samples have a uniquedistribution of limiting species as shown in FIG. 17 and Table 2.However, each limiting species can ultimately be address byprecipitation within a hygroscopic cooling system. Thus, hygroscopiccooling systems can productively use waste water such as reverse osmosisconcentration.

Additional Embodiments

The following exemplary embodiments are provided, the numbering of whichis not to be construed as designating levels of importance:

Embodiment 1 provides a method for heat dissipation using a hygroscopicworking fluid, the method comprising:

transferring thermal energy from a heated process fluid to thehygroscopic working fluid in a process heat exchanger, to form a cooledprocess fluid;

condensing liquid from a feed gas on a heat transfer surface of a feedgas heat exchanger in contact with the cooled process fluid, to form acooled feed gas, the heated process fluid, and a condensate;

dissipating thermal energy from the hygroscopic working fluid to acooling gas composition with a fluid-air contactor;

transferring moisture between the hygroscopic working fluid and thecooling gas composition with the fluid-air contactor; and

adding at least part of the condensate to the hygroscopic working fluid.

Embodiment 2 provides the method of Embodiment 1, wherein the cooledprocess fluid has sub-ambient temperature

Embodiment 3 provides the method of any one of Embodiments 1-2, whereinthe condensing of the liquid from the feed gas comprises transferringthermal energy from the feed gas to the cooled process fluid.

Embodiment 4 provides the method of any one of Embodiments 1-3, furthercomprising feeding the cooled feed gas to a rotary mechanical device.

Embodiment 5 provides the method of any one of Embodiments 1-4, furthercomprising feeding the cooled feed gas to a turbine.

Embodiment 6 provides the method of any one of Embodiments 1-5, furthercomprising feeding the cooled feed gas to a combustion turbine.

Embodiment 7 provides the method of any one of Embodiments 1-6, whereinthe feed gas comprises the ambient atmosphere, a gas having more watervapor than the ambient atmosphere, a gas having less water vapor thanthe ambient atmosphere, or a combination thereof.

Embodiment 8 provides the method of any one of Embodiments 1-7, whereinthe feed gas heat exchanger and the process heat exchanger are parts ofa turbine inlet chilling system (TIC).

Embodiment 9 provides the method of any one of Embodiments 1-8, whereinthe process heat exchanger comprises a condenser of a refrigerationcycle.

Embodiment 10 provides the method of any one of Embodiments 1-9, whereinthe process heat exchanger is a chiller that moves thermal energy fromthe heated process fluid to the hygroscopic working fluid via a chillerworking fluid.

Embodiment 11 provides the method of Embodiment 10, wherein the chillercomprises a compressor that compresses a chiller working fluid prior totransferring thermal energy from the compressed chiller working fluid tothe hygroscopic working fluid.

Embodiment 12 provides the method of Embodiment 11, wherein the chillertransfers heat directly from the compressed chiller working fluid to thehygroscopic working fluid without any intermediate heat exchangers andwithout any intermediate heat transfer medium.

Embodiment 13 provides the method of any one of Embodiments 11-12,wherein the chiller comprises a valve that allows the chiller workingfluid to expand prior to transferring thermal energy from the heatedprocess fluid to the expanded chiller working fluid.

Embodiment 14 provides the method of any one of Embodiments 1-13,wherein the condensing of the liquid from the feed gas providessufficient condensate to make up for water lost from the hygroscopicworking fluid to the cooling gas composition in the fluid-air contactor,providing at least water-neutral operation.

Embodiment 15 provides the method of any one of Embodiments 1-14,wherein a rate of formation of the condensed liquid is equal to orgreater than a rate than a rate of moisture mass transfer between thehygroscopic working fluid and the cooling gas composition in thefluid-air contactor.

Embodiment 16 provides the method of any one of Embodiments 1-15,wherein over 24 hours, the total amount of the condensate generated bythe method is equal to or exceeds the total amount of water lost fromthe hygroscopic working fluid during the method.

Embodiment 17 provides the method of any one of Embodiments 1-16,further comprising storing the cooled process fluid in a process fluidstorage area for a period of time before placing the cooled processfluid in the feed gas heat exchanger.

Embodiment 18 provides the method of Embodiment 17, wherein the periodof time the cooled process fluid is stored for is about 1 minute toabout 7 days.

Embodiment 19 provides the method of any one of Embodiments 1-18,further comprising storing the condensate for a period of time prior toadding the condensate to the hygroscopic working fluid.

Embodiment 20 provides the method of Embodiment 19, wherein the periodof time the condensate is stored for is about 1 minute to about 10years.

Embodiment 21 provides the method of any one of Embodiments 1-20,further comprising maintaining the hygroscopic working fluid to preventcrystallization of the desiccant from the desiccant-based hygroscopicworking fluid.

Embodiment 22 provides the method of any one of Embodiments 1-21,wherein the cooling gas composition comprises the ambient atmosphere.

Embodiment 23 provides the method of any one of Embodiments 1-22,wherein the cooling gas composition comprises a gas having more watervapor than the ambient atmosphere, a gas having less water vapor thanthe ambient atmosphere, or a combination thereof.

Embodiment 24 provides the method of Embodiment 23, wherein the gashaving more or less water vapor than the ambient atmosphere comprises atleast one ambient air into which water has been evaporated by misting orspraying, an exhaust stream from a drying process, an exhaust stream ofhigh-humidity air displaced during ventilation of conditioned indoorspaces, an exhaust stream from a wet evaporative cooling tower, and aflue gas stream from a combustion source and the associated flue gastreatment systems.

Embodiment 25 provides the method of any one of Embodiments 1-24,wherein dissipating thermal energy from the hygroscopic working fluid tothe cooling gas composition comprises dissipating thermal energy fromthe hygroscopic working fluid to the ambient atmosphere using thefluid-air contactor and dissipating thermal energy from the hygroscopicworking fluid to a gas having either less water vapor or more watervapor than the ambient atmosphere using the fluid-air contactor.

Embodiment 26 provides the method of any one of Embodiments 1-25,wherein transferring moisture between the hygroscopic working fluid andthe cooling gas composition comprises transferring moisture between thehygroscopic working fluid and the ambient atmosphere using the fluid-aircontactor and transferring between the hygroscopic working fluid and agas having either less water vapor or more water vapor than the ambientatmosphere using the fluid-air contactor.

Embodiment 27 provides the method of any one of Embodiments 1-26,wherein the hygroscopic working fluid is a low-volatility hygroscopicworking fluid.

Embodiment 28 provides the method of any one of Embodiments 1-27,wherein the hygroscopic working fluid comprises an aqueous solutioncomprising at least one of sodium chloride (NaCl), calcium chloride(CaCl₂)), magnesium chloride (MgCl₂), lithium chloride (LiCl), lithiumbromide (LiBr), zinc chloride (ZnCl₂), sulfuric acid (H₂SO₄), sodiumhydroxide (NaOH), sodium sulfate (Na₂SO₄), potassium chloride (KCl),calcium nitrate (Ca[NO₃]₂), potassium carbonate (K₂CO₃), ammoniumnitrate (NH₄NO₃), ethylene glycol, diethylene glycol, propylene glycol,triethylene glycol, dipropylene glycol, and any combination thereof.

Embodiment 29 provides the method of any one of Embodiments 1-28,wherein the hygroscopic working fluid comprises an aqueous solutioncomprising calcium chloride (CaCl₂)).

Embodiment 30 provides the method of any one of Embodiments 1-29,wherein the fluid-air contactor operates in at least one relative motionincluding countercurrent, cocurrent, or crossflow operation.

Embodiment 31 provides the method of any one of Embodiments 1-30,wherein the fluid-air contactor is enhanced by at least one of forced orinduced draft of the cooling gas composition by a powered fan, naturalconvection airflow generated from buoyancy differences between heatedand cooled air, and induced flow of the cooling gas compositiongenerated by the momentum transfer of sprayed working fluid into thecooling gas composition.

Embodiment 32 provides the method of any one of Embodiments 1-31,wherein the cooling gas composition comprises humidity from at least oneof a spray, mist, or fog of water directly into the cooling gascomposition, an exhaust gas stream from a drying process, an exhaust gasstream consisting of high-humidity rejected air displaced during theventilation of conditioned indoor spaces, an exhaust airstream from awet evaporative cooling tower, and an exhaust flue gas stream from acombustion source.

Embodiment 33 provides the method of any one of Embodiments 1-32,wherein the feed gas comprises humidity from at least one of a spray,mist, or fog of water directly into the feed gas composition, an exhaustgas stream from a drying process, an exhaust gas stream consisting ofhigh-humidity rejected air displaced during the ventilation ofconditioned indoor spaces, an exhaust airstream from a wet evaporativecooling tower, and an exhaust flue gas stream from a combustion source.

Embodiment 34 provides the method of any one of Embodiments 1-33,wherein the heat transfer from the feed gas is enhanced by addition ofmoisture to the hygroscopic working fluid using at least one of:

direct addition of liquid water to the hygroscopic working fluid;

absorption of relatively pure water directly into the hygroscopic fluidthrough the forward osmosis membrane of a forward osmosis waterextraction cell;

absorption of vapor-phase moisture by the working fluid from amoisture-containing gas stream outside of the process air contactorwhere the moisture-containing gas stream including at least one ofambient air into which water has been evaporated by spraying or mistingflue gas from a combustion source and its associated flue gas treatmentequipment;

exhaust gas from a drying process;

rejected high-humidity air displaced during ventilation of conditionedindoor air; and

an exhaust airstream from a wet evaporative cooling tower.

Embodiment 35 provides the method of any one of Embodiments 1-34,wherein the process heat exchanger is cooled by a flowing film of thehygroscopic working fluid enabling both sensible and latent heattransfer to occur the transferring of thermal energy from the heatedprocess fluid.

Embodiment 36 provides the method of Embodiment 35, wherein the processheat exchanger is placed at the inlet to the fluid-air contactor forraising humidity levels of the cooling gas composition.

Embodiment 37 provides the method of any one of Embodiments 35-36,wherein the process heat exchanger is placed at the outlet of said aircontactor for lowering humidity of the cooling gas composition.

Embodiment 38 provides the method of any one of Embodiments 1-37,wherein transferring moisture between the hygroscopic working fluid andthe cooling gas composition comprises using a working fluid-aircontactor and a vacuum evaporator.

Embodiment 39 provides the method of any one of Embodiments 1-38,wherein transferring moisture between the hygroscopic working fluid andthe cooling gas composition comprises the use of a forward osmosismembrane of a forward osmosis water extraction cell.

Embodiment 40 provides a method for heat dissipation using a hygroscopicworking fluid, the method comprising:

transferring thermal energy from a heated process fluid to thehygroscopic working fluid in a process heat exchanger, to form a cooledprocess fluid;

transferring thermal energy from the feed gas to the cooled processfluid in a feed gas heat exchanger, to form a cooled feed gas and theheated process fluid;

feeding the cooled feed gas to a combustion turbine;

dissipating thermal energy from the hygroscopic working fluid to acooling gas composition with a fluid-air contactor; and

transferring moisture between the hygroscopic working fluid and thecooling gas composition with the fluid-air contactor.

Embodiment 41 provides a method for heat dissipation using a hygroscopicworking fluid, the method comprising:

transferring thermal energy from a heated process fluid to thehygroscopic working fluid in a chiller, to form a cooled process fluid;

condensing liquid from a feed gas on a heat transfer surface of a feedgas heat exchanger in contact with the cooled process fluid, to form acooled feed gas, the heated process fluid, and a condensate, wherein

-   -   the chiller comprises a compressor that compresses a chiller        working fluid prior to transferring thermal energy from the        compressed chiller working fluid to the hygroscopic working        fluid, and    -   the chiller comprises a valve that allows the chiller working        fluid to expand prior to transferring thermal energy from the        heated process fluid to the expanded chiller working fluid;

feeding the cooled feed gas to a combustion turbine;

dissipating thermal energy from the hygroscopic working fluid to acooling gas composition with a fluid-air contactor, the cooling gascomposition comprising the ambient atmosphere;

transferring moisture between the hygroscopic working fluid and thecooling gas composition with the fluid-air contactor; and

adding at least part of the condensate to the hygroscopic working fluid;

wherein the condensing of the liquid from the feed gas providessufficient condensate to make up for water lost from the hygroscopicworking fluid to the cooling gas composition in the fluid-air contactor,providing at least water-neutral operation.

Embodiment 42 provides a system for heat dissipation using a hygroscopicworking fluid, the system comprising:

a process heat exchanger configured to transfer thermal energy from aheated process fluid to a hygroscopic working fluid to form a cooledprocess fluid;

a feed gas heat exchanger configured to condense liquid from a feed gason a heat transfer surface of the feed gas heat exchanger in contactwith the cooled process fluid, to form a cooled feed gas, the heatedprocess fluid, and a condensate; and

a fluid-air contactor configured to dissipate heat from the hygroscopicworking fluid to a cooling gas composition, and configured to transfermoisture between the hygroscopic working fluid and the cooling gascomposition;

wherein the system is configured to add at least part of the condensateto the hygroscopic working fluid.

Embodiment 43 provides the system of Embodiment 42, wherein the feed gasheat exchanger and the process heat exchanger are parts of a turbineinlet chilling system (TIC).

Embodiment 44 provides the system of any one of Embodiments 42-43,wherein the process heat exchanger comprises a condenser of arefrigeration cycle.

Embodiment 45 provides the system of any one of Embodiments 42-44,wherein the process heat exchanger is a chiller that moves thermalenergy from the heated process fluid to the hygroscopic working fluidvia a chiller working fluid.

Embodiment 46 provides the system of Embodiment 45, wherein the chillercomprises a compressor that is configured to compress a chiller workingfluid prior to transferring thermal energy from the compressed chillerworking fluid to the hygroscopic working fluid.

Embodiment 47 provides the system of Embodiment 46, wherein the chilleris configured to transfer heat directly from the compressed chillerworking fluid to the hygroscopic working fluid without any intermediateheat exchangers and without any intermediate heat transfer medium.

Embodiment 48 provides the system of any one of Embodiments 46-47,wherein the chiller comprises a valve that is configured to allow thechiller working fluid to expand prior to transferring thermal energyfrom the heated process fluid to the expanded chiller working fluid.

Embodiment 49 provides the system of any one of Embodiments 42-48,wherein the system is configured to operate in at least water-neutraloperation with respect to moisture loss from the hygroscopic workingfluid and moisture gain from the condensate.

Embodiment 50 provides the system of any one of Embodiments 42-49,further comprising a process fluid storage area configured to store thecooled process fluid for a period of time before placing the cooledprocess fluid in the feed gas heat exchanger.

Embodiment 51 provides the system of any one of Embodiments 1-50,wherein the system is configured to maintain the hygroscopic workingfluid to prevent crystallization of the desiccant from thedesiccant-based hygroscopic working fluid.

Embodiment 52 provides a method of waste water disposal, the methodcomprising:

contacting a hygroscopic working fluid with a heat exchanger having aheated process fluid;

transferring thermal energy from the heated process fluid to thehygroscopic working fluid and flowing the hygroscopic working fluid fromthe heat exchanger to a fluid-air contactor having an air stream;

contacting the hygroscopic working fluid with the air stream of thefluid-air contactor;

transferring water from the hygroscopic working fluid to the air stream,collecting the resulting hygroscopic working fluid and circulating it tothe process heat exchanger;

directing at least a portion of the hygroscopic working fluid to form amixture with waste water in a makeup mix tank at conditions toprecipitate dissolved impurities from the mixture; and

filtering the precipitate from the mixture to form a filtrate anddirecting the filtrate to combine with the circulating hygroscopicworking fluid;

wherein the hygroscopic working fluid comprises a desiccant and water.

Embodiment 53 provides the system of embodiment 52, wherein the wastewater comprises a reverse osmosis concentrate, a concentrated saltstream, a scrubbing liquor from an industrial process, a blowdown from acooling tower, or a mixture thereof.

Embodiment 54 provides the system of embodiment 52 or 53, wherein thewaste water comprises a concentrated effluent from a water treatmentsystem, a desalination system or a reverse osmosis system.

Embodiment 55 provides the system of any one of embodiments 52-54,wherein the mass concentration of desiccant in the makeup mix tank is atleast about 5%.

Embodiment 56 provides the system of any one of embodiments 52-55,wherein the mass concentration of desiccant in the makeup mix tank is atleast about 15%.

Embodiment 57 provides the system of any one of embodiments 52-56,wherein the fluid-air contactor is a hygroscopic cooling tower.

Embodiment 58 provides the system of any one of embodiments 52-57,wherein the fluid-air contactor and air stream are configured totransfer an amount of water from the hygroscopic working fluid to theair stream about equal to an amount of waste water that is added to thehygroscopic working fluid.

Embodiment 59 provides the system of any one of embodiments 52-58,wherein the hygroscopic working fluid comprises an aqueous solutioncomprising at least one of sodium chloride (NaCl), calcium chloride(CaCl₂)), magnesium chloride (MgCl₂), lithium chloride (LiCl), lithiumbromide (LiBr), zinc chloride (ZnCl₂), sulfuric acid (H₂SO₄), sodiumhydroxide (NaOH), sodium sulfate (Na₂SO₄), potassium chloride (KCl),calcium nitrate (Ca[NO₃]₂), potassium carbonate (K₂CO₃), ammoniumnitrate (NH₄NO₃), ethylene glycol, diethylene glycol, propylene glycol,triethylene glycol, dipropylene glycol, and any combination thereof.

Embodiment 60 provides a hygroscopic cooling system, the systemcomprising:

a hygroscopic working fluid comprising a desiccant and water;

a heat exchanger to transfer thermal energy from a heated process fluidto the hygroscopic working fluid;

a fluid-air contactor having an air stream, wherein the fluid-aircontactor and air-stream are configured to transfer water from thehygroscopic working fluid to the air stream;

wherein the heat exchanger and the fluid-air contactor are configured sothe hygroscopic working fluid is circulated through the heat exchangerand the fluid-air contactor;

a makeup mix tank configured to receive waste water and at least some ofthe circulated hygroscopic working fluid, wherein the makeup mix tank isat conditions which permit the waste water and the hygroscopic workingfluid to mix and to precipitate dissolved impurities from the resultingmixture; and

a filter unit configured to remove precipitated impurities from themixture of waste water and hygroscopic working fluid and direct theresulting filtrate to combine with the circulated hygroscopic workingfluid.

Embodiment 61 provides the hygroscopic cooling system of Embodiment 60,wherein the waste water comprises a reverse osmosis concentrate, aconcentrated salt stream, a scrubbing liquor from an industrial process,a blowdown from a cooling tower, or a mixture thereof.

Embodiment 62 provides the hygroscopic cooling system of Embodiment 60or 61, wherein the waste water comprises a concentrated effluent from awater treatment system, a desalination system or a reverse osmosissystem.

Embodiment 63 provides the hygroscopic cooling system of any one ofEmbodiments 60-62, wherein the mass concentration of desiccant in themakeup mix tank is at least about 5%.

Embodiment 64 provides the hygroscopic cooling system of any one ofEmbodiments 60-63, wherein the mass concentration of desiccant in themakeup mix tank is at least about 15%.

Embodiment 65 provides the hygroscopic cooling system of any one ofEmbodiments 60-64, wherein the fluid-air contactor is a hygroscopiccooling tower.

Embodiment 66 provides the hygroscopic cooling system of any one ofEmbodiments 60-65, wherein the fluid-air contactor and air stream areconfigured to transfer an amount of water from the hygroscopic workingfluid to the air stream about equal to an amount of waste water addedthat is to the hygroscopic working fluid.

Embodiment 67 provides the hygroscopic cooling system of any one ofEmbodiments 60-66, wherein the hygroscopic working fluid comprises anaqueous solution comprising at least one of sodium chloride (NaCl),calcium chloride (CaCl₂)), magnesium chloride (MgCl₂), lithium chloride(LiCl), lithium bromide (LiBr), zinc chloride (ZnCl₂), sulfuric acid(H₂SO₄), sodium hydroxide (NaOH), sodium sulfate (Na₂SO₄), potassiumchloride (KCl), calcium nitrate (Ca[NO₃]₂), potassium carbonate (K₂CO₃),ammonium nitrate (NH₄NO₃), ethylene glycol, diethylene glycol, propyleneglycol, triethylene glycol, dipropylene glycol, and any combinationthereof.

Embodiment 68 provides the hygroscopic cooling system of any one ofEmbodiments 60-67, further comprising:

a reverse osmosis system which accepts untreated water and produces atreated water effluent and a reverse osmosis concentrate,

wherein the reverse osmosis concentrate is directed to the makeup mixtank via a conduit to provide the waste water.

Embodiment 69 provides the hygroscopic cooling system of any one ofEmbodiments 60-68, further comprising:

a desalination system which accepts brackish water and produces atreated water effluent and a concentrated salt stream,

wherein the concentrated salt stream is directed to the makeup mix tankvia a conduit to provide the waste water.

Embodiment 70 provides the hygroscopic cooling system of any one ofEmbodiments 60-69, further comprising:

a second heat exchanger to transfer thermal energy from a second heatedprocess fluid to the heated process fluid;

a second fluid-air contactor having a second air stream configured totransfer thermal energy, water, or a combination thereof, from theheated process fluid to the second air stream, wherein the secondfluid-air contactor produces a blowdown stream which is collected anddirected to the makeup mix tank via a conduit to provide the wastewater; and

wherein the heated process fluid is a non-hygroscopic working fluidcirculated between the second heat exchanger and the second fluid-aircontactor.

Embodiment 71 provides the hygroscopic cooling system of any one ofEmbodiments 60-70, wherein the second fluid-air contactor is aconventional cooling tower.

Embodiment 72 provides the method or system of any one or anycombination of Embodiments 1-71 configured to provide waste water asmakeup water for hygroscopic working fluid.

Embodiment 73 provides the method or system of Embodiment 72 configuredto evaporate approximately all waste water provided as makeup water tothe hygroscopic working fluid.

Embodiment 74 provides the method or system of any one or anycombination of Embodiments 1-73 optionally configured such that allelements or options recited are available to use or select from.

The invention claimed is:
 1. A method of reducing liquid concentratedischarge from a process that generates waste water, the methodcomprising: contacting a hygroscopic working fluid with a heat exchangerhaving a heated process fluid and a fluid-air contactor having an airstream, wherein the hygroscopic working fluid comprising a desiccant andwater; transferring thermal energy from the heated process fluid to thehygroscopic working fluid via the heat exchanger, and flowing thehygroscopic working fluid from the heat exchanger to the fluid-aircontactor; contacting the hygroscopic working fluid with the air streamof the fluid-air contactor; transferring water from the hygroscopicworking fluid to the air stream, collecting the resulting hygroscopicworking fluid and circulating it to the process heat exchanger;directing waste water away from the process that generates waste waterto form a mixture in a makeup mix tank with at least a portion of thehygroscopic working fluid, at conditions to precipitate dissolvedimpurities from the mixture; and filtering the precipitate from themixture to form a filtrate and directing the filtrate to combine withthe circulating hygroscopic working fluid; wherein the waste water is aconcentrated salt stream comprising a dissolved solid species; andwherein the mixture in the makeup mix tank provides a maximum solubilitylimit for the dissolved species that is less than half that of themaximum solubility limit in the waste water.
 2. The method of claim 1,further comprising evaporating water from the hygroscopic working fluidin the fluid-air contactor.
 3. The method of claim 1, wherein the heatexchanger is configured to thermally drive evaporation of water from thehygroscopic working fluid corresponding to the amount of waste waterprovided.
 4. The method of claim 1, wherein the waste water furthercomprises a scrubbing liquor from an industrial process, a blowdown froma cooling tower, or a mixture thereof.
 5. The method of claim 1, whereinthe mass concentration of desiccant in the makeup mix tank is at leastabout 5%.
 6. The method of claim 1, wherein the mass concentration ofdesiccant in the makeup mix tank is at least about 15%.
 7. The method ofclaim 1, wherein the fluid-air contactor is configured to transfer anamount of water from the hygroscopic working fluid to the air streamabout equal to an amount of waste water that is added to the makeup mixtank.
 8. The method of claim 1, wherein the hygroscopic working fluidcomprises an aqueous solution comprising at least one of sodium chloride(NaCl), calcium chloride (CaCl₂)), magnesium chloride (MgCl₂), lithiumchloride (LiCl), lithium bromide (LiBr), zinc chloride (ZnCl₂), sulfuricacid (H₂SO₄), sodium hydroxide (NaOH), sodium sulfate (Na₂SO₄),potassium chloride (KCl), calcium nitrate (Ca[NO₃]₂), potassiumcarbonate (K₂CO₃), ammonium nitrate (NH₄NO₃), ethylene glycol,diethylene glycol, propylene glycol, triethylene glycol and dipropyleneglycol.
 9. The method of claim 1, wherein the waste water has higher TDSthan the hygroscopic working fluid.
 10. The method of claim 1, whereinthe process that generates waste water resultingly achieves zero liquidconcentrate discharge to the environment.
 11. The method of claim 3,wherein the process that generates waste water resultingly achieves zeroliquid concentrate discharge to the environment.
 12. The method of claim1, wherein the process that generates waste water is a desalinationprocess.
 13. The method of claim 1, wherein the process that generateswaste water is a desalination process and the process that generateswaste water resultingly achieves zero liquid concentrate discharge tothe environment.
 14. A hygroscopic cooling system for reducing liquidconcentrate discharge from a system that generates waste water, thesystem comprising: a heat exchanger to transfer thermal energy from aheated process fluid to a hygroscopic working fluid, wherein thehygroscopic working fluid comprises a desiccant and water; a fluid-aircontactor having a air stream to transfer water from the hygroscopicworking fluid to the air stream; a conduit to transfer a waste waterfrom a system that generates waste water to a makeup mix tank configuredto receive the waste water and at least some of the circulatedhygroscopic working fluid, wherein the makeup mix tank is at conditionswhich permit the waste water and the hygroscopic working fluid to mixand to precipitate dissolved impurities from the resulting mixture; anda filter unit configured to remove precipitated impurities from themixture of waste water and hygroscopic working fluid and direct theresulting filtrate to combine with the circulated hygroscopic workingfluid; wherein the waste water is a concentrate salt stream comprising adissolved solid species; and wherein the mixture in the makeup mix tankprovides a maximum solubility limit for the dissolved species that isless than half that of the maximum solubility limit in the waste water.15. The hygroscopic cooling system of claim 14, wherein the heatexchanger is configured to thermally drive evaporation of water from thehygroscopic working fluid corresponding to the amount of waste waterprovided.
 16. The hygroscopic cooling system of claim 14, wherein thewaste water further comprises a scrubbing liquor from an industrialprocess, a blowdown from a cooling tower, or a mixture thereof.
 17. Thehygroscopic cooling system of claim 14, wherein the fluid-air contactoris configured to transfer an amount of water from the hygroscopichygroscopic working fluid to the air stream about equal to an amount ofwaste water that is added to the makeup mix tank.
 18. The hygroscopiccooling system of claim 14, wherein the hygroscopic working fluidcomprises an aqueous solution comprising at least one of sodium chloride(NaCl), calcium chloride (CaCl₂)), magnesium chloride (MgCl₂), lithiumchloride (LiCl), lithium bromide (LiBr), zinc chloride (ZnCl₂), sulfuricacid (H₂SO₄), sodium hydroxide (NaOH), sodium sulfate (Na₂SO₄),potassium chloride (KCl), calcium nitrate (Ca[NO₃]₂), potassiumcarbonate (K₂CO₃), ammonium nitrate (NH₄NO₃), ethylene glycol,diethylene glycol, propylene glycol, triethylene glycol and dipropyleneglycol.
 19. The hygroscopic cooling system of claim 14, wherein thesystem that generates waste water achieves zero liquid concentratedischarge to the environment as a result of the waste water transfer.20. The hygroscopic cooling system of claim 14, wherein the system thatgenerates waste water is a desalination system.